A review of the Cucurbitaceae

C. JEFFREY

Royal Botanic Gardens,

Kew,Richmond, Surrey

Accepted forpublication March 1980

I ' I . I ) ~ I ( ' \ \ 1 1 1 \1ii(ti(.\ ot (;u(ui~bitdCeae \iIice 1964 is reviewed, particulai attention h n g paid to lhr
I-oles of seed-coat anatomy, palynology and phytochemistry in elucidating the taxononiv of the
lamily; to the use of wild species and land-races as sources of horticulturally desirable traits for the
iiiiprweiiient o f crops; to the potentialities of wild species for domestication as new crops for tropical
ai-eas, and to the biology of reproduction, sex control and sex expression. The classification of the
l a d y is outlined, illustrated by discussion of the more important members ofeach tribe, and a revised
( lassific-ationof Cucumis is presented.

KEY WORDS: - crop improvement - Cucumis - Cucurbitaceae - Horal biolog\. - new crops -
palynologv- phytochemistT- seed-coat anatomy- sex control - sex expression - taxonomy.

CONTENTS

Inti-(iductioti . . . . . . . . . . . . . . . . . . . . . . . L' '3 3

Taxonomy . . . . . . . . . . . . . . . . . . . . . . 234
Palvnology . . . . . . . . . . . . . . . . . . . . . 23 i
Seeii-coat ariatotny . . . . . . . . . . . . . . . . . . . . :'I;
Phytochciriistr) . . . . . . . . . . . . . . . . . . . . . 23 i
Srrd oils and proteins . . . . . . . . . . . . . . . . . . . . 2.36
Cytogenetitr . . . . . . . . . . . . . . . . . . . . . . . LYO
Zanoiiioidear . . . . . . . . . . . . . . . . . . . . . 236
Cuc-urliitoidrar . . . . . . . . . . . . . . . . . . . . . . 3 7
Melothiieae . . . . . . . . . . . . . . . . . . . . . 2s7
Schizoprponear . . . . . . . . . . . . . . . . . . . . . 2-10
Joliffkar , . . . . . . . . . . . . . . . . . . . . . 24 I
Ti-idios;inthear . . . . . . . . . . . . . . . . . . . 11 I
Bcnincaseae . . . . . . . . . . . . . . . . . . . 24 1
Cucurbiteae . . . . . . . . . . . . . . . . . . . . . 243
Cvclanther-eae , . . . . . . . . . . . . . . . . . . . 244
Sicyocacs , . . . . . . . . . . . . . . . . . . 14',
Rcfc~i-riiccs . . . . . . . . . . . . . . . . . . . . . 24>:

INTRODUCTION
The Cucurbitaceae is a moderately large family of about 130 genera and 900
species. An outline classification, giving subfamilies, tribes and major subtribes
and genera, is given in Table 1. All Cucurbitaceae are frost-sensitive and the
family is confined to the warmer parts of the globe; those few that extend to
233
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234 C. JEFFREY

temperate regions either winter underground as tubers below frost level, or are
annuals and pass the winter as seeds. The family is most abundantly represented
within the tropics, especially in tropical Africa and the neotropics. In tropical
Africa, it is especially characteristic of the drier regions and is rather poorly
developed in the rain-forest floras; by contrast, in the neotropics and
Indomalesia, it is best developed in the rain-forest areas and there are com-
paratively few in the drier regions.
Man has had a long and intimate association with this family, and this
association is of longest standing (c. 15 000 years B J . 1 and of greatest economic
importance in the warmer regions. In such regions Cucurbitaceae are found in
almost every vegetable garden and are important items in the diet. In
archeological deposits seeds and fruit-rinds are identifiable to the genus and
often to the species. The family is notable for the comparatively large number of
species known only in cultivation. This paper reviews developments since the
survey given by Jeffrey ( 1967a).
- __.__
__/

TAXONOMY
Considerable progress has been made in the alpha-taxonomy of the family.
Modern floras have recently been produced for most of tropical Africa (Fernandes,
1976; Fernandes & Fernandes, 1970; Jeffrey, 1967b, 1978a; Keraudren, 1967;
Keraudren-Aymonin, 1975a; Roessler, 19681, for Madagascar (Keraudren, 19661,

Table 1. Outline classification of the Cucurbitaceae

I. Subfamily ZANONIOIDEAE u=X.

Feuillea

11. subfamily CUCURBITOIDEAE

Tribe 1 . Melolliric;ic ) i = 12( 13, 1 1 , 7 )
. subtribe Melothriinae
Melothria, Zehneria, Cucumeropsis, Posadaea, M elancium,
Cucumis
subtribe Dendrosicyoinae
Apodanthera, Kedrostis, Corallocarpus, Iberuillea
subtribe Guraniinae
Gurania, Psiguria
Tribe 2. .Sc lii~opcpoiicac )I= 10
.$I / / l ~ l l / l i ~ / l l / / i

Tribe 3. ,jc~lillic;ic I / = 14, I I , 9

. l I i i t n i i ~ & ~ i , /'/il~idiatitha,felfnirin
Tribe 4 . .Iii[Iio\.iilllir;ie ii=Il(I2)
I J-II /io\aut/w\, / / u d p u i i i u , ,4/npelu~icyo~
Tribe 5. l % c ~ i i i i i c ~ i \ c a !cI = I P ( I 1 , 13, 10)
subtribe Benincasinae
Coccinia, Benincara, Lagemria, Citrullus, Acanthosicyos,
Praecitrullus
subtribe Luffinae
Luffa
Tribe 6. (:iic-ui-l)ilcw. / I = 20
Cur urOit(i, S l t n n l i . C q a p u n m
Tribe I. ~;\cl;llllllcl~cac n = x
(,:ufiintl i r w , .I Jmrah, Eln/pnop \i \, RytidostyliJ
Tribe 8. Sic\cic;ic u = 12
~ S ~ i h i w S/ ii, g w
 CUCURBITACEAE 235

Indo-China (Keraudren-Aymonin, 1975b), Guatemala (Dieterle, 19761, Panama

(Wundcrlin, 1978) and Venezuela (Jeffrey & Trujillo, in press). The family is least
well-known in eastern Asia, Indomalesia and the rest of the neotropics. In stark
contrast to this flurry of floras is the complete lack of modern monographic
treatments. N o major genus, not even the most economically important, has been
revised in its entirety within the last fifty years. Nevertheless, our taxonomic un-
derstanding of the family has advanced, and progress has been greatly aided by
developments in palynology, seed-coat anatomy and phytochemistry.

PALYNOLOGY

The palynological diversity of the family has been amply demonstrated by

recent studies (Alyoshina, 1966, 1967, 1968, 197 1 ; Keraudren, 1968). Particular
pollen grain character-states are found to characterize taxa ranging in rank from
subfamily through tribe and subtribe to groups of genera, genera and groups of
species.

SEED-COAT ANATOMY

The functional seed-coat is exotestal (Corner, 19761, derived entirely from the
outer epidermis of the outer integument of the ovule. The mature exotesta
generally consists of'three layers: SEED EPIDERMIS, generally but not always one cell
thick, the cells inay be cuboid o r radially e1ongated;SEED H Y P O D E R M I S , of one to
n i a t i y layers of' variously thick-walled, lignified and pitted cells; and a
S < : L l : K I - N ( : t f Y M A ~ r 0 1 ~ S L A Y E R , usually one cell thick, of thick-walled, lignified arid
pitted cclls, wtiicti niay be radially elongated o r tangentially elongated and
appearing square i t i cross-section (Fursa, 1974; Getahun, 1973; Hardy, 1976;
Singti, D., 196.5, 1971; Singh & Dathan, 1972, 1973, 1974a, b, c, d, 1976). In
tievelopinetit and structure, the seeds of Cucurbitaceae are unlike those of'
Passillol-accac and Cariraceae, to which families they have been considered by
sonic autlrors t o Ijc related.

PHYTOCH EM ISTRY

Biochemically, the Cucurbitaceae are characterized by the presence of

cucurbitacins and other triterpenoids (Hylands & Salama, 1979) in the vegetative
parts and fruits, and by the occurrence in the seeds of free amino acids, seed oils
and storage proteins.
The cucurbitacins are the bitter principles of the Cucurbitaceae and are
oxygenated tetracyclic triterpenes (Gibbs, 1974; Kupchan, Morris, Haim
Meshuiam & Sneden, 1978). The occurrence of different cucurbitacins in
dilli~rcntparts 01' the plant, either free or as glycosides, has been shown t o be of'
taxonomic significance. Where the genetics of bitterness has been investigated, as
in Lagenaria, Citrullus, Cucumis and Cucurbita, a single dominant gene for bitterness
Iias l>cctid c s c r i l d in each case (Robinson, Munger, Whitaker & Bohn, 1976).
The free amino acids of the seeds have been investigated to a limited extent;
eight have been identified, and a large number of other of ninhydrin-positive
compounds recorded (Dunhill 8c Fowden, 1965; Fowden, 1965). Citrulline has
been found in all genera investigated ; other ninhydrin-positive compounds have
more restricted distributions which are of significance taxonomically. Nothing is
236 C. JEFFREY

known of the role of these free amino acids and ninhydrin-positive compounds
in nature; possible they may function as chemical defence mechanisms, since the
embryos containing these substances are otherwise highly nutritious and lack
cucurbitacins.

SEED OILS AND PROTEINS

The nutritive value of the seeds stems from their high oil and protein contents.
The seed oils of Cucurbitaceae fall into two groups, one with palmitic-oleic-lino-
leic acid composition, the other with conjugated triene acids-punicic acid and
a-cleostearic acid (Azeemoddin & Rao, 1967; Chisholm & Hopkins, 1967). The
taxonomic significance of this difference is as yet unclear; there is cor-
respondence with some genera and subtribes; others are variable in this respect.
The seed proteins of Cucurbitaceae are comparable in nutritive value to those
of the Leguminosae (Thornson, Weber, Berry 8c Bemis, 1978; Tu, Eustace 8c
Deyoe, 1978); though, like other plant proteins, they tend to be low in lysine and
the sulphur-containing amino acids. They are generally richer in methionine
than those of the legumes, and selective enrichment may be a possibility in some
cases. Physico-chemical characterization of the seed storage albumins is in its
infancy, but so far, those from different species within a genus have been found
to be very similar and the overall amplitude of variation small (Pichl, 1978).
Serologically, the Cucurbitaceae relate to the Datiscaceae and Begoniaceae, and
show no affinity with the Loasaceae, the Caricaceae or the Violales (Passifloraceae,
Violaceae, Flacourtiaceae, Turneraceae) (Kolbe8cJutta, 1979).

CYTOGENETICS

Cytologically, the Cucurbitaceae are difficult to study and only fairly recently
have good methods been devised (Varghese, 1973). Basis chromosome numbers
for the different major taxa vary widely-8, 10, 1 1 , 12, 20-and other numbers
are also known- 7 , 13, 14 (seeTable 1). Polyploidy is ofmore frequent occurrence
than was previously supposed, but is still comparatively infrequent and does not
seem to have played an important part in the generic evolution of the family. The
nomenclature of the genes of the major cultivated species has recently been
standardized; there are now at least 68 genes known to control qualitative
characters in Cucumis sativus L., 37 in C. melo L., 25 in Citrullus lanatus (Thunb.)
Mats. & Nakai, and 30 in the cultivated Cucurbita species (Robinson et al., 1976).
Thc Cucurbitaceae exhibit an interesting range of sex-expression. Most spccics
are dioecious, monoecious, or andromonoecious ; sex-expression may often be
variable within the genus and can also vary within the species (Frankel 8c Galun,
197 7). Monoecy and the very rare hermaphroditism are more characteristic of'
annual than of perennial species, especially of those which inhabit the climatic
extremes of the family range.

ZANONIOIDEAE

This is by far the smaller of the two subfamilies, with about 1 7 genera (six in
the New World). It is poorly known taxonomically, especially in south-east Asia
where most genera occur. It is little exploited economically; Fevillea is used as an
 CUCURBITACEAE 23 7

o i l source in some indigenous neotropical cultures. The subfamily is charac-

terized by free styles, apically bifid tendrils and small striate pollen grains.
Interestingly, the Zanonioideae appear to exhibit all the typical cucurbitaceous
lkatur-cs t o a lesser degree than do the Cucurbitoideae; e.g. the internal phloem
of the vascular bundles develops late o r not at all, few cucurbitacins are know,
and only citrulline of the seed amino acids is recorded. Interestingly also, apart
from the monotypic Actinostemma which extends to the climatic extreme of the
subfamily range in N.E. China, Korea and Japan, and a Sicydium species recently
tliscovcrcd i n Mexico, most are perennial and dioecious. Dioecy has generally
beeti considered a derived condition in the family, but as a working hypothesis,
the postulate that dioecy represents the ancestral condition and monoecy,
andromonoecy and hermaphroditism successively derived states of sex-
expression, deserves consideration.
n1c seeds of Zanoriioideae differ from those of the Cucurbitoideae in two ways
(Singh & Dathan, 1974a). The cells of the sclerenchymatous layer divide
periclinally as well as anticlinally, so that the sclerenchyma comes to be
composed of small brachysclerids instead of large osteosclerids o r asterosclerids;
and the aerenchyma, derived from the cells below the ovule epidermis, becomes
strongly thickened and lignified.

CUCURBITOIDEAE

The Cucurbitoideae are characterized by a single style with only the stigmas
more o r less free, and by proximally 2-5 -branched o r unbranched tendrils. They
are palynologically diverse and divisible into 8 tribes (Table 11, which will be
reviewed separately below.

Melothrieae
This is the largest tribe with 34 genera, 16 in the New World. It is characterized
by reticulate, tricolporate or tripororate pollen grains, small flowers with more o r
less campanulate hypanthia, and unelaborated anther-thecae. Generic limits are
still unclear in places and it is uncertain if any genera occur in both the Old and
New Worlds. KPdroJtiJ (Old World), Corallocarpus (Old World), and Zbervillea (New
World) share a distinctive seed-coat anatomy, in which the hypodermis is absent
along the faces of the seeds (Singh 8c Dathan, 1 9 7 4 ~ )Corallocarpus
. boehmii (Cogn.)
C. Jeffrey is reported as anomalous by these authors and needs reinvestigation.
Similai- uncertainty exists over the genera Zehneria (Old World) and Melothria (New
World). Their separation is not supported by their seed-coat anatomy (Singh &
Dathan, 1974b), but is supported by differences in seed amino-acids (Fowdcn,
1965). More species need to be investigated in these respects before firm
conclusions can be drawn.
The tribe has a number of species which have potential as new crops, and
which would repay further investigation; for the humid tropics, Cucumeropsis
iiiniinii Naud. (used as an oil and protein source in west Africa) and its New World
;ttialoguc Po.,ndaea .sphaerocarpa Cogn., both annuals; for wooded grassland areas,
the ct-ccpitig, tendril-less Melancium campestre Naud. of Brazil and Paraguay; and
for aridand semi-arid areas, Apodanthera undulata A. Gray of the southern U.S.A.
and Mexico (Berry, Bemis, Weber 8c Dreher, 1978).
238 C. JEFFREY

Cucumis is the most important genus with two major crops, C. sativus L.
(cucumber) and C. me10 L. (melon) and two minor crops, C. anguria L. (West
Indian Gherkin) and C. metul@-us Naud. (horned cucumber). Its taxonomy has
recently been elucidated by both classical and cytotaxonomic methods (Dane &
Tsuchya, 1976; Deakin, Bohn & Whitaker, 1971; Kroon, Custers, Kho, Nijs 8c
Vatekamp, 1979). I t can be divided into five cross-sterile species groups in two
subgenera, as formally established below.
Cucumis L., Sp. Pl.: 101 l(1753)& Gen. P1. ed. 5 : 442 (1754).

I. subgenus Cucumis
Monoecious or andromonoecious; n= 7 ; 3 or 4 Sino-Himalayan species,
including C. satiuus L., C. hystrix Chakr. (syn C. muriculatus Chakr.).
11. subgenus Melo (Miller)C.Jeffrey, comb. et stat. nov.
Melo Miller, The Gardeners Dictionary Abridgement ed. 4. (1754). About 25
species, mostly in tropical and south Africa; n= 12.
1. ‘metuliferus’group.
Monoecious annuals with red spiny fruits-one species, C. melu1ifrru.r
Naud.
2. ‘anguria’ group.
Dioecious, monoecious or andromonoecious perennials or monoecious
or androinonoecious annuals with yellowish or brown-striped spiny
fruits-about 20 species, closely related, forming in many cases
partially fertile hybrids-includes C. anguria L., C. dipsaceus Spach, C.
prophetarum L., C. myriocarpus Naud. and C. sacleuxii Paill. & Bois.
3. ‘melo’ group.
Monoecious or andromonoecious perennials or annuals with smooth
Iruits--4 species, C. melo L., C . trigonus Roxb., C. sagittatus Peyr. (syn. c.
angolensis Cogn., C. dinteri Cogn.), C. hum$+-uctusStent.
4. ‘hirsutus’ group.
Dioecious perennials with smooth orange fruits-one species, C.
hirsutus Sond.

Some wild species exhibit traits that it would be desirable to transfer

genetically to the cultivated species, e.g. resistance to various nematodes, insects,
mites, pathogenic fungi, bacteria and viruses (Greber, 1978 ; Peterson, 1975 ;
Prowidenti & Robinson, 197 7 ) . Unfortunately, transfer of genes from wild
species to C. sativus and C . melo has yet to be accomplished (Fassuliotis, 1977;
Kroon et al., 1979). Crosses of C. melo with C. sagzttatus, for example, yield only
partially developed seeds (Deakin et al., 197 1 ) .
In the case of C . satiuus (De Ponti, 1978), a species with very restricted
distribution i n the wild, the as yet unstudied wild Sino-Himalayan species C.
hystrix should be examined for its properties and crossability with C. sativus. C.
melo, in contrast, is very widespread in the wild and has a wealth of local wild
variants and cultivated land-races. Indian variants have provided sources of
tesistance to powdery mildew (SphaerothecafulgzneaSchecht. ex Fr. Poll.), downy
niildew (Pseudoperonospora cubensis (Berk. & Curt. Rost.) and watermelon mosaic
 CUCURBITACEAE 239

virus 1 (Peterson, 1975; Whitaker, 1979), and some Indian and African races are
being used in the development of crop resistance to leafininer (Liriomyzasatiuae
Blanch.) (Kennedy, Bohn, Stoner & Webb, 1978) and melon aphid (Aphis gossypii
Glov.) (Kishaba, Bohn & Toba, 1976); the genetics and chemistry of aphid
resistance are under study. C. melo is divisible into two major infraspecific taxa, a
wiclcyread tropical one with closely purberulous ovaries (C. mdo var. agrestis
Naud.), and a more restricted south-west Asian one with tomentose ovaries (C.
melo var. melo), which might more properly be considered as subspecies. The
melon cultivars of commerce are derived from domesticates of the latter; by
contrast, indigenous Indian and Sino-Japanese cultivars and land-races appear
to be-a result of at least two independant domestications of the tropical taxon. In
this diverse history lies the basis of the utility of the tropical races in providing
germ plasm for the commercial cultivars, the genetic bases of which are
considerably narrower.
The genera most closely related to Cucumis are Cucumella, Oreosyce,
Myrmecosicyos, Mukia and Dicoelospermum, all as yet unexplored as possible gene
sources ; the correct taxonomic position of Dicoelospermum has only recently been
established (Singh, 1965).
T l l C need li>r high yields, uniformity of crop, simultaneity of cropping and
suitability lix mechanical harvesting has prompted much research into economic
nietliocls of'producing F, hybrid cultivars in C. satiuus. As a result, the genetics and
c.heriiistry of' sex-expression are better-known in C. satiuu5 than in any other
cur.url,it (Berinan, Feldinan 8c Galun, 1977; Frankel 8c Galun, 1977; Kubicki,
1972). Sex control is autosomal, and the genes controlling sex-expression are of
two types. Gene M controls a trigger mechanism that permits only stamen or pistil
tlevelopnient ; Howers of MI- plants are therefore unisexual; flowers of m/m plants
may Ijc hermaphrodite. The second type of gene controls the flowering pattern,
wliicli i n C. ~ a t i u u sis (in the main shoot) an initial strong male tendency which
gradually changes into a strong female tendency. One gene of this type, st, brings
Ii~~nalcncss closer to the base of the plant; another, a, has the opposite effect. The
main sex types that result are: androecious 3 (MI-, st+/st+,a/a); monoecious (SQ
(MI-, s t + / s t + , A/-); gynoecious Q (MI-, st/st, A/-; andromonoecious dQ (m/m,
s t + / s t + , A / - ) ; and hermaphrodite Q (m/m, stlst, A/-). M is completely dominant,
but ~licrcis no complete dominance in the st gene; the st+/stheterozygote shows an
intei-mediate phenotype and its expression is strongly affected by environmental
1ktot.s; a is fully expressed only in M/-, st+/st+ genotypes. The main shoot
ilowcring pattern'in nionoecious plants is made up of three phases-I, in which
m;rlc Ilowcrs ai-eproduced at the nodes; 11, in which there is a mixture ofmale and
ii.inale nodes; and 111, in which female flowers are producxd a ( thc nodes. Other
types lack o i i v o r two of these phases.
Sexual differentiation is closely connected with the balance of growth
substances in the vicinity of the developing flower-bud (Friedlander, Atsmon 8c
Galun, 1977). The different responses of the different sex genotypes may be
explained by an optimum curve hypothesis; they behave in the same way, but
respond differently to different concentration-ranges of endogenous growth
substances. Artificial modification of sex-expression is possible by way of
application of growth substances, or by changes in environmental conditions
that affect endogenous concentrations. Long days, high temperatures and
applied gibberellins tend to extend the male phase; short days, low
240 C. JEFFREY

temperatures, applied auxins, ethylene-yielding compounds and growth

retardants tend to accelerate the initiation of the female phase. I t is thus possible
to induce genetically gynoecious plants to produce abundant staminate flowers
by the application of gibberellic acid, and genetically androecious plants to
produce pistillate flowers by treatment with 2-chloroethylphosphonic acid.
Spraying with gibberellic acid is used in the production of commercial F, hybrid
seed to produce and maintain the gynoecious seed-parent line (Frankel & Galun,
1977).
Sex-expression in C. melo is under similar control, differing however in detail
(Frankel &Galun, 1977; Loy, Natu, Zack & Fritts, 1979).
The subtribe Guraniinae contains some of the most interesting and unusual
cucurbits. Unlike most cucurbits, which have flimsy, ephemeral, white or yellow
flowers, Guruniu and Psiguria have tough, long-lived orange, red or pink flowers.
These facts suggest ornithophily, and indeed hummingbirds regular1 visit the
li
[lowers(Condon, pers. comm.). However, they are also visited by butter ies of the
genus Heliconius, which collect pollen from the flowers, mix it with a liquid
(probably nectar), thus inducing it to pregerminate and release amino acids into
solution, and then ingest the amino acids. As a result, unlikemost butterflies, adult
female Heliconius are long-lived (up to 6 months) and exhibit the long-term, open-
ended oogenesis characteristic of insects whose reproduction depends upon adult
feeding (Dunlap-Pianka, Boggs & Gilbert, 1977). Larval stages are passed on
PussiJ7ora spp.
Psiguriu and Gurunia are the only cucurbit genera that shed pollen in tetrads
(Marticorena, personal communication). All Gurunia and all but one Psiguriu
species do so; the one Psiguriu species that sheds single grains is otherwise
practically indistinguishable from a tetrad-shedding species. Although Gurania
and P.@uria are closely related and similar in pollination biology, they have
evolved diff’erent vector attractant syndromes. In Pszguria the hypanthium and
sepals are green as in other cucurbits and the petals form the main attractant,
whereas in Gurania, the petals are yellow guiding structures and the colour is
developed in the hypanthium and sepals.
A number of problems, currently under study, is raised by these
observations- the evolutionary relationship between Gurunia and Psiguriu; the
co-evolutionary relationships between the cucurbits and Heliconius and
hummingbirds as pollinators; the significance of the particular type of sex-
expression and female inflorescence morphology in the subtribe; and the
significance of tetrad-shed pollen (Condon, pers. comm.).

Schizopeponeae
This is the smallest tribe of the family, characterized by small, reticuloid pollen
grains, and made up of a single genus, Schizopepon, with 5 species, 4 in the
Himalaya and southern China, which are dioecious, and 1 species with
hermaphrodite flowers, occuring in the northern extremity of the climatic range
of the family in Japan, Korea, N.E. China and the Soviet Far East. A comparative
investigation of the genetics of sex-expression in the genus is much to be desired.
 CUCURBITACEAE 24 1

Joliffieae
This is a rather heterogenous Old World tribe of five genera, which are in many
ways the least specialized of the Cucurbitoideae. Some Thladiantha species, alone in
the Cucurbitoideae, have the apically bifid tendrils of the zanonioid type. One of
these, T. grosuenorii (Swingle) C. Jeffrey, a traditional medicinal plant of southern
China, has an intensely sweet fruit, owing to the presence of a glycoside, which may
have potential for development as a non-calorific sweetner (Jeffrey, 1979).
Momordica is a large genus; some species, e.g. M . cochinchinensis (Lour.)Sprengel, M .
dioecu-RGb., M . cymbalaria Hooker fil. (syn. M . tuberosa Roxb. (Azeemoddin & Rao,
1967) and cs ecially ,M. charantia L. (Williams & Ng, 1976) are cultivated as
T
vegetables or ruits. Cucurbitacins are absent from Momordica, and the bitterness of
M . chururitia is due to an alkaloid, momordecine. From this species, a substance
with t h e clinical properties of insulin has also been isolated (Baldwa, Bhandari,
Pangaria & Go$, 197 7 ) . Momordica seed-oils are characterized by conjugated
ti.icwc acids (Azeeinoddin & Rao, 1967).
The east African Teyairiapedata (Sims) Hooker is cultivated commercially as an
oil seed (oyster-nut). In view of the desirability of eliminating the need to dehusk
the seeds, which is a commercial disadvantage, the thinner-husked west African
species T . occidentalis Hooker fil. should be explored as a source of genes. Also,
the possibility of a naked-seed mutant should be borne in mind. Such a mutant is
known in Cucurbita pep0 L., in which a single major recessive gene controls the
iiakd-seed character (Robinson et al., 1976).The seeds lack a testa, the embryo
being enclosed by the nucellus alone.

Trichosantheae
This Old Word tribe of 10 genera is characterized by elongated hypanthia in
both male and female flowers, and is divisible into a number of palynologically
well-marked subtribes. The monotypic Hodgsonia (lard fruit) is grown for its large
edible seeds in Indomalesia, while the seeds of wild Ampelosicyos species are used
similarly in Madagascar. Trichosanthes is the largest genus; it is quite diverse in
seed-coat anatomy (Singh & Dathan, 1976) and poorly known taxonomically.
The cultivated species--. dioeca Roxb. and T . cucumerina L. var. anguina (L.)
Haines (snake gourd) -appear more o r less isolated within the genus. T . kirilowii
Maxim. (eastern Asia) is under investigation as the source of the mid-gestation
abortifacient trichosanthin, a basic protein with a molecular weight of about
18000 (Shanghai Institute of Experimental Biology Second Laboratory, 1976;
Tiaji, Gae, Zhou, Zhu & Cai, 1977).

Benincaseae
Characterized generally by reticulate, tricolporate pollen grains, this tribe of
16 genera is practically confined to the Old World. Benincasa (Indomalesia,
I / = 12) aiiti Praecitrullus (India, n= 12) are both monotypic genera with their
only species cultivated and unknown in the wild. The fruit of Benincasa hispida
(Thunb.) Cogn. has a thick flesh, mild flavour and (because of its waxy coat)
outstanding storage qualities with high resistance to spoilage; also, the plants are
prolific and grow rapidly. Although now grown mainly as a household crop, it has
242 C. JEFFREY

potential as an important new crop for large areas of moderately dry Africa and
Latin Aiiierica (Ayensuetal., 1975).
Coccinia (n= 12) has about 30 species, confined to tropical Africa, except
C. grandis (L.) Voigt (syn. C. indica W. 8c A.), which extends throughout the
palaeotropics. This genus is also cultivated in India. Coccinia grandis is the only
cucurbit in which a heteromor hic bivalent associated with sexual difference has
B
been found (Roy, 1974). It is ioecious, the male is the heterogamic sex with an
XY chromosome pair, the Y chromosome being longer than the X chromosome. It
is probable that the Y chromosome carries a dominant female suppressor and a set
of genus controlling male development. There is also evidence that other genes are
involved in sex-expression, and that at least some of these are carried on the
autosomes (Ugale, D’Cruz & Patil, 1976). Interestingly, a related species recently
discovered in Ghana is the only naturally monoecious Coccinia species known.
Coccinia abyssinica (Lam.)Cogn. is cultivated in parts of Ethiopia for its edible tubers
(Getahun, 1973).I t also grows wild; the tubers ofwild plants are inedible, but the
fruits are eaten; conversely, the fruits of cultivated plants are not eaten.
.-La,genaria (n= 1 1 ) has one cultivated annual monoecious species and five wild
perennial dioecious species, the latter confined to Africa and Madagascar. The
cultivated species, L. siceraria (Mol.) Standley, the bottle gourd, has an
archeologically documented association with man dating back to prehistoric times
in both the Old and the New Worlds. Use of the dried fruits as containers was
important in pre-ceramic cultures (Whitaker, 1971). Recent work (Heiser, 1973a)
has confirmed the existence of two subspecies, one in Asia, the other in Africa and
the New World. Overall, the evidence suggests that the species was originally wild
in Africa and Asia (thus giving Lugenaria a generic distribution similar to that of
Coccinia, Diplocyclos and Citrullus in this tribe, having a number of species in Africa,
one of which extends throughout the palaeotropics); that its spread to the New
World was by oceanic drift of gourds across the Atlantic and their propagation by
early New World man; that it was domesticated independently at least three times,
in Asia, Africa and South America; and that later seed commerce has now partially
obscured the original geographical subspecific distinction, for example, in
Trinidad, Arizona and New Guinea (Heiser, 1973b).Though hybridization with at
least one perennial wild species, L. sphuerica (Sond.) Naud., is known, the hybrid is
sterile and the possibility of the transfer of desirable traits to the cultivated species
requires investigation.
CitruLlus (n= 11) is a genus of three species, one of which, C. lanatus (Thunb.)
Mats.”&-Nakai (syn. C. vulgaris Eckl. & Zeyh.), the watermelon, is an important
crop. It was in this crop, that the transfer of disease resistance from an inedible
land-race to horticulturally acceptable cultivars was first demonstrated
(Whitaker, 1979); this work on Fusarium wilt by W. A. Orton in the early 1900’s
cited in Whitaker 1979, opened the door for crop improvement by the transfer of
disease resistant germplasm from wild species or feral forms into cultivated
species. C. Lanatus can hybridize with the perennial C.colocynthis (L.)Schrad. (Singh,
A. K., 1978), so gene transfer between the two is feasible. C. colocynthis has
characteristics and potentialities as a new arid-land crop very similar to those of
Cucurbitafoetidissima A. Gray (Ayensuet al., 1975)and warrants similar exploration.
Perhaps even more promising as an arid-land crop is Acanthosicyos naudinianus
(Sonti.)C. JefTrey (n= 1 I ) , a plant used as a source offood and water in the Kalahari
rcgion.
 CUCURBITACEAE 243

The one exception to the entirely Old World distribution of the Benincaseae is
the genus Luffa, which has two wild Old World species, two cultivated Old World
species, and one wild New World species. It is also exceptional in the tribe in its
fruit structure and operculate dehiscence, and seed-coat anatomy (Singh, D.,
197 1 ) . In both these respects it resembles the tribe Cyclanthereae, and it has been
suggested it may form a link between this tribe and the Benincaseae. This
possibility is supported by the seed amino-acids (Dunnill & Fowden, 1965). Luffa
and Cyclanthereae have only citrulline and m-carboxyphenylalanine, while the
latter is absent in other Benincaseae (except Cogriauxia) which (again except
Cogniauxia) have P-pyrazol- 1 -ylalanine and a-glutamyl-/I-pyrazol- 1 -ylalanine.
kio~vcvci-,the basic chroinosoine number (n= 13) differs from those o f the
Benincaseae ( 1 1 , 12, 10) and Cyclanthereae (8).

Cucurbi teae
The Cucurbiteae are characterized by large, spiny, pantoporate pollen grains,
and except for 1 species of Cayaponia in west Africa and Madagascar, all 12 genera
are confined to the New World. The cultivated species-Sicana odorfera Well.)
Nauct. (cassabanana) and 5 Cucurbita species (pumpkins, squashes, marrows),
C. p p p o L., C. inixta Pang., C. maxima Lam., C. moschata (Lam.) Poir. and C.jicfolia
Bouchc (all except the last, annuals)--are known only in cultivation and formed
one of' the staples of the squash -beans-maize cultures of the pre-Columbian
N c w World (Whitaker & Cutler, 1965). Cucurbita has also about 20 wild species,
mostly in Central America. Numerical taxonomic (Rhodes, Bemis, Whitaker &
Carmer, 19681, seed anatomical (Singh 8c Dathan, 1973) and cytogenetic studies
(Whitaker & Bemis, 1965) show that the Cucurbita species can be arranged into
9 9-1-oups, 2 xerophytic and 7 mesophytic. Two genera of solitary bees,
Peponapis and Xenoglossa, derive their entire sustenance from the nectar and pollen
of Cucurbita. Evidence from the taxonomy, distribution and behaviour of these
bees (Hurd, Linsley & Whitaker, 197 11, taken in conjunction with archeological
and genetical data (Whitaker & Bemis, 1975) suggests that Cucurbita is native in
South as well as in Central America; that the ancestral Cucurbita were mesophytic
annuals; that C. moschata is closest to the ancestral taxon and has been
tlornesticated independently in Central and South America, and that
C. maxima, C. ficfolia, C. mixta and C. pep0 were originally domesticated respectively
in South America, Central America south of Mexico, Mexico south of Mexico
City, and (probably)Mexico north of Mexico City.
While there are barriers to hybridization between the species of Cucurbita, no
species (or species group) is completely isolated from all other species. Some wild
species have horticulturally desirable traits ; C . LundelLiana Bailey has resistance to
powticry Inildew; C. ecuadorensis Cutler & Whitaker and C. foptidiJsima A. Gray
have resistance to cucumber mosaic virus, watermelon mosaic virus 1 and
watermelon mosaic virus 2 (Prowidenti, Robinson & Munger, 1978). Simple
wild x cultivated autopolyploids leave the entire genome of the wild species
intact, with all its concomitant undesirable traits. Work is therefore in progress
on the transfer of single chromosomes from the wild species to the genomes of
cultivated species (Bemis, 1973). Genome analysis by use of isozyme markers has
been used to study relationships, e.g. in the cross C.ecuadorensis x C. maxima (Wall
& Whitaker, 197 1 ) . It is a promising method, especially when applied to a genus
244 C. JEFFREY

like Cucurbita with numerous small, similar chromosomes, that can give evidence
of’ cryptic chromosomal structural differences. The related genera Sicana,
Tecunumania, Peponopsis, Calycophysum, Polyclathra and Schizocarpon are all as yet un-
investigated for desirable horticultural traits and the feasibility of their
transference to the cultivated Cucurbita species.
An exciting development is the attempt being made to produce an ‘instant’
domesticated plant using C. foetidissimu, a xerophytic perennial species native in
northern Mexico and southern U.S.A. Like Citrullus colocynthis and Acanthosicyos
naudinianus, it has a number of features which favourably predispose it to such
exploitation. It is a perennial plant of regions of low rainfall; it produces an
abundant crop of fruit, containing seeds rich in oil and protein; it lends itself to
mechanical harvesting; it produces a large storage root, rich in extractable
starch, and it readily reproduces vegetatively by rooting at the nodes (Ayensu, el
al., 1975; Bemis, Berry, Weber & Whitaker, 1978; Bemis, Curtis, Weber & Berry,
1978; Thomson et al., 1978; Tu et al., 1978). Wild populations consist either
entirely of monoecious plants or of monoecious and gynoecious plants in an
approximately 1 : 1 ratio. This is perhaps brought about b y a dominant gene for
gynoecy restricted to the heterozygous state, the monoecious being the
lioniozygous recessive (Bemis, Berry et al., 1978). The development programme
has involved plant collection, physical and chemical evaluation of the seed,
selection, research and breeding for high yield, seed production, and evolution of
a cropping system. The drought and heat tolerance of this species should make it
adaptallle to cultivation on the two-thirds of the world’s land surface that have
arid o r semi-arid climates.

Cyclanthereae
The Cyclanthereae, an entirely New World tribe of 12 genera, is characterized
by operculate or explosively dihiscent, 1-2-carpellate fruits, polycolporate pollen
grains, and seed-coats with the sclerenchymatous layer composed of radially
elongated osteosclerids (Singh & Dathan, 1972). Two species of Cyclanthera, C.
brachystuchya (Ser.) Cogn. (syn. C. explodens Naud.) and C. pedata (L.) Schrad., the
latter known only in cultivation, are especially useful as vegetables for the upland
tropics (at 1500-2000, and 2000-3000 m, above sea level respectively).
Elateriopsis is night Howering and its large flowers exhibit clearly one of‘ the
interesting features of the Cucurbitaceae, a marked similarity of form of the
anthers and stigmas. Associated with this is frequent complicated folding of the
anther-thecae and/or close adhesion or connation of the filaments and/or
anthers, the functional significance of which is yet to be explained. Cucurbit
flowers produce nectar (or sometimes oil) as well as (in the male) pollen, and the
whole syndrome is perhaps associated, in this predominantly unisexually-
flowered family, with the need for male and female flowers to look alike, i.e. to
present a similar visual-attractant stimulus to a potential vector. Rytidostylis is
unusual in the tribe in having flowers with elongated hypanthia and
asymmetrically colporate pollen grains.
 CUCURBITACEAE 245
Sicyoeae
This tribe with six genera is confined to the New World and Hawaii (apart
Ii-oiii one species of Sicjos in Australasia). I t is characterized by one-seeded fi-uits
and polycolporate spiny pollen grains. The only important crop species is
Sechium edule (Jacq.) Sw., the chayote, a vigorous perennial, known only in
cultivation, of which all parts-seeds, fruits, leaves and rootstock-are edible
(Giusti, Resnik, Del v. Ruiz & Grau, 1978). The single overgrown seed germinates
in situ. Until recently, Sechium was thought to be monotypic, without wild
relatives, but it is now clear that there are about eight wild species in Central
America (including one semi-cultivated), with fruits ranging from woody to
fleshy (Jeffrey, 1978b). The way is therefore now open for exploration of their
relationships, hybridization and breeding. The other genera of the tribe have
small, usually leathery or woody fruits and are poorly understood taxonomically.

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