E D I N B U R G H J O U R N A L O F B O T A N Y 64 (2): 117–129 (2007) 117

E Trustees of the Royal Botanic Garden Edinburgh (2007)

doi:10.1017/S0960428607000844

THREE NEW SPINY EUPHORBIA

(EUPHORBIACEAE) SPECIES FROM WESTERN
SAUDI ARABIA

A . A . F AYED1 & D . A . A L- Z AHRANI2

Three shrubby, succulent, spiny Euphorbia (Euphorbiaceae) species from western Saudi
Arabia are described and illustrated as new: Euphorbia madinahensis Fayed & D.Al-
Zahrani, Euphorbia saudiarabica Fayed & D.Al-Zahrani and Euphorbia taifensis Fayed &
D.Al-Zahrani. Diagnostic characters, descriptions and taxonomic comments on each are
given, and they are compared with closely related species. The geographical distribution
of the three new species is shown.

Keywords. Arabian Peninsula, distribution, Euphorbia, Saudi Arabia, taxonomy.

In preparation for an account of the genus Euphorbia L. (Euphorbiaceae) in the

Arabian Peninsula, three new shrubby, succulent, spiny species from western Saudi
Arabia are here described.

N EW S PECIES

Euphorbia madinahensis Fayed & D.Al-Zahrani, sp. nov. Figs 1, 2, 5.

Euphorbia aff. cactus Ehrenb.: Collenette, Ill. Guide Fl. Saudi Arabia 239 (1985);
Collenette, Euphorbia J. 4: 102–122 (1987); Collenette, Wildfl. Saudi Arabia 309–
310 (1999).
Frutex succulentus spinosus usque ad 1.5 m altus, in omni parte glaber; caules
copiose ramosi, praesertim a basi, fasciculos densos ramorum usque ad 3 m vel
plus latos facientes; rami flavovirentes fere erecti usque ad 35(–45) cm in
circumscriptio, manifeste constricti in segmenta pyriformia (9–15 cm longa et
prope basin 20–25 cm in circumscriptio), 3–5-anguli lateribus fere parallelis,
angulis spinis gemellis in margine continuo corneo griseo 17 mm distantibus et
circa 11 mm longis, interdum ad basin aculeolis parvis rudimentalibus instructis.
Foliorum rudimenta simplicia sessilia cordata 5 6 3 mm, apice mucronato,
margine integro, mox decidua. Cyathia terna aggregrata, centrale masculo (raro
bisexuali) sessili primum florente, lateralibus bisexualibus in pedicellis 5–7 mm
longis, crescentibus masculum centralem occultantibus; cymae involucraque
1
Botany Department, Faculty of Science, Assiut University, Assiut, Egypt.
2
Science Department, Jeddah Teacher’s College, PO Box 15758, Jeddah 21454, Saudi Arabia; e-mail:
dhaferalzahrani@hotmail.com. Present address: Plant Sciences, School of Biological Sciences, Faculty of
Life Sciences, University of Reading, Reading RG6 6AS, UK; e-mail: d.a.alzahrani@reading.ac.uk
118 A. A. FAYED & D. A. AL-ZAHRANI

F I G . 1. Euphorbia madinahensis Fayed & D.Al-Zahrani: mature plant (A) and close-up of
branch (B) at Jabal Al-Ahmar.

bracteata, bracteis triangularibus 3–5.5 6 6–8 mm apice acuto margine fimbriato.

Involucrum campanulatum, 6–7 mm latum 5–6 mm profundum; glandulae
cyathiorum flavae patentes transverse elliptico-oblongae 2–2.5 6 5–7 mm, lobis
marginalibus margine breviter fimbriatis. Flores masculi pedicello 4.2 mm longo,
 A B

F I G . 2. Euphorbia madinahensis: close-up of flowering branch (A) and fruiting branch (B) at Jabal Al-Ahmar.
NEW EUPHORBIA SPECIES FROM SAUDI ARABIA
119
120 A. A. FAYED & D. A. AL-ZAHRANI

bracteolis circa 3.5 mm longis, in dimidio superiore dissectis. Flore feminei sessiles
vel subsessiles, ramis stylorum circa 3 mm longis infra connatis per circa 1 mm, ad
apicem bifidis. Capsula lobis 3 rotundatus, circa 1.8 cm lata, matura e rubro
viridis. Semina grisea subglobosa 3.5–4 mm longa laevia. – Type: Saudi Arabia:
Al-Figrah highland, 95 km west of Madinah, 2000–2200 m alt., 16 xi 1998, D. Al-
Zahrani 185 (holo M; iso BM, CAI, E, K, KAAU1, KSU).

Succulent spiny shrub, up to 1.5 m tall, glabrous in all parts; stems branching freely,
especially from the base, to form dense clumps up to 3 m or more in diameter;
branches yellow-green, almost erect, up to 35(–45) cm in circumference, distinctly
constricted into pear-shaped segments (9–15 cm long and 20–25 cm in circumference
near the base), 3–5-angled, with nearly parallel sides; angles with paired spines on
continuous horny grey margins; spines 17 mm apart and c.11 mm long, with
occasional small rudimentary prickles at the base. Leaf rudiments simple, sessile,
cordate, 5 6 3 mm, apex mucronate, margin entire, soon deciduous. Cyathia in
groups of three; the central male, rarely bisexual, sessile, flowering first; the lateral
bisexual, with 5–7 mm long pedicel, obscuring the male cyathium as they develop;
cymes and involucres bracteate; bracts triangular, 3–5.5 6 6–8 mm, with acute apex
and fimbriate margin. Involucre campanulate, 6–7 mm across, 5–6 mm deep; cyathial
glands yellow, patent, transversely elliptic-oblong, 2–2.5 6 5–7 mm; marginal lobes
with short fimbriate margin. Pedicel of male flowers 4.2 mm long; bracteoles c.3.5 mm
long, dissected in the upper half. Female flower sessile to subsessile; style arms c.3 mm
long, connate for c.1 mm below, bifid at apex. Capsule with 3 rounded lobes, c.1.8 cm
across, ripening reddish green. Seeds grey, subglobose, 3.5–4 mm long, smooth.

Distribution. Euphorbia madinahensis is named after Madinah city where the species
is endemic to the nearby highlands (Fig. 5), namely Figrah, Al-Ahmar, Anagayn,
Auf and Reem (1050–2350 m alt.). These highlands appear to be the northern limit
for spiny euphorbias in Arabia (Collenette, 1987).

Habitat and flowering times. On granite mountains with sparse rainfall, from 1050 to
2350 m alt. Flowering and fruiting from September to February.

Vernacular names. Karath, Karathah.

Conservation status. According to the IUCN Red List Categories and Criteria,
version 3.0 and 3.1 (IUCN, 2001, 2003), this new species should be considered
Vulnerable (VU) under criteria B1ab (i,ii,iii,iv,v) + 2ab (i,ii,iii,iv,v) based on
observations and inferences that it has both an extent of occurrence of less than
20,000 km2 and an area of occupancy of less than 2000 km2. It is known to exist at no
more than 10 locations and is in continuing decline.

1
King Abdulaziz University herbarium, Jeddah, Saudi Arabia, proposed abbreviation.
 NEW EUPHORBIA SPECIES FROM SAUDI ARABIA 121

T A B L E 1. Comparison of morphological characters in Euphorbia madinahensis and E. cactus

Character E. madinahensis E. cactus

Habit Up to 1.5 m tall, 1.5–3 m in Up to 3 m tall, 2 m in width
width
Branches
– Colour Yellow-green Dark green
– Angles 3–5, rounded, or subacute 3 rarely 4, acute
– Shape Pear-shaped segments Wing-like, compressed angles
– Circumference 20–25 cm 25–35 cm
– Width of angle 5–8 cm 15–20 cm
Spine size 2–11 mm long, 17 mm apart 10–25 mm long, 40 mm apart
Bracts 3–5.5 6 6–8 mm 2.5–3.5 6 5 mm
Capsule
– Size 10 6 18 mm 8–9 6 15–16 mm
– Shape Triangular, rounded Triangular, acute
– Pedicel 2 mm 2–5 mm

Euphorbia madinahensis is closely related to Euphorbia cactus Ehrenb. It has

correspondingly very stout, fleshy, yellow-green stems, with subacute angles and
distinct pear-shaped segments. They are not mottled with radiating yellow streaks (a
characteristic of Euphorbia cactus Ehrenb.). In addition, the branch margins of the
new species are almost without undulations, while the spines are white and stout,
being linked by a contiguous, grey band. The cymes cover the entire apical segments,
so that the plants appear to carry balls of flowers. Moreover, the cyathia are
subsessile and are subtended by triangular, obviously larger bracts. A morphological
comparison between Euphorbia madinahensis and E. cactus is given in Table 1.
Collenette (1985, 1987, 1999) was aware of most of the abovementioned differences
and named the plants of these populations Euphorbia sp. aff. cactus Ehrenb.

Specimens examined. SAUDI ARABIA. Figrah highland, 95 km W of Al-Madinah, 2000–2200 m

alt., D. Al-Zahrani 176 (BM, E, K, KAAU, M); idem, 1 xi 1998, D. Al-Zahrani 184 (KAAU,
KSU, RIY); Jibal Reem, c.20 km N of Al-Musayjid, Madinah–Badr Hunain road, 1560 m alt.,
7 viii 1998, D. Al-Zahrani 174 (BM, E, KAAU, KSU, M, RIY); Jibal Anagayn, c.15 km NW
of Al-Musayjid, Madinah–Badr Hunain road, 1900 m alt., 9 viii 1998, D. Al-Zahrani 177 (K,
KSU); Jabal Auf, 80 km SSW of Madinah, 1170 m alt., 26 xi 1986, Collenette 5945 (K, RIY);
Jabal Al-Ahmar, c.100 km SW of Madinah, on a barren rocky hillside, 2300 m alt., 24 ii 1998,
D. Al-Zahrani 152 (BM, CAI, E, K, KAAU, KSU, M, RIY).

Euphorbia saudiarabica Fayed & D.Al-Zahrani, sp. nov. Figs 3, 5.

Frutex vel arbor parva candelabriformis succulenta spinosa, non magis quam 3 m
alta, in omni parte glabra, caule principali unico (45–60 cm in circumscriptio);
rami flavovirentes vel flavi, longi crassi graciles simplices 3–5-anguli 15–19 cm
in circumscriptio, inferiores declinantes, terram verrentes, dein assurgentes,
122 A. A. FAYED & D. A. AL-ZAHRANI

F I G . 3. Euphorbia saudiarabica Fayed & D.Al-Zahrani: mature plant (A) and close-up of
fruiting branch (B) at Thahban (between Al-Birk and Al-Qahmah).

superiores fere erecti, lateribus fere parallelis, spinis gemellis in scutis parvis non
contiguis, apice nigro, 1 cm longis, interdum ad basin aculeolis parvis
rudimentalibus instructis. Foliorum rudimenta sessilia simplicia ovata, interdum
lamina oblique truncata, apice acuto, margine integro, mox decidua. Cyathia
terna aggregrata, centrale masculo (raro bisexuali) sessili primum florente,
lateralibus bisexualibus in pedicellis 2–4 mm longis, crescentibus masculum
 NEW EUPHORBIA SPECIES FROM SAUDI ARABIA 123

centralem occultantibus; cymae involucraque bracteata, bracteis 1.5–2 6 1–

1.5 mm, apice rotundato, margine fimbriato. Involucrum campanulatum, 4.5 mm
latum 3.5 mm profundum; glandulae cyathiorum flavae transverse oblongae 2.5–
3.5 6 1–1.5 mm, lobis marginalibus margine breviter fimbriatis. Flores masculi
pedicello 3.5 mm longo, bracteolis 3 mm longis, supra dissectis. Flore feminei
pedicellati, pedicello 2–4 mm longo, ovario in stipite notabiliter reflexo, ramis
stylorum 2 mm longis, infra connatis per 1 mm, ad apicem bifidis. Capsula lobis 3
rotundatus, 4 6 6–6.5 mm, in stipite 14 mm longo notabiliter reflexo. Semina
subglobosa 2.5–3 6 2–2.3 mm grisea laevia. – Type: Saudi Arabia: Between Al-
Birk and Al-Qahmah, 55 km N of Shoqaiq–Muhayil junction, Al-Qunfudhah–
Jizan road, 10 m alt., 5 vi 1998, D. Al-Zahrani 164 (holo M; iso BM, E, K, M).

A candelabra-like succulent spiny shrub or small tree, not exceeding 3 m tall,

glabrous in all parts, with a single main stem (45–60 cm in circumference); branches
yellow-green to yellow, long, stout, slender, simple, 3–5-angled, 15–19 cm in
circumference, the lower branches arching down to sweep the ground then turning
upwards, the upper ones almost erect; branch (sides) nearly parallel, with paired
spines on small, non-contiguous spine shields; spines black-tipped, 1 cm long, with
occasional small rudimentary prickles at the base. Leaf rudiments sessile, simple,
ovate, sometimes with obliquely truncate lamina, apex acute, margin entire, soon
deciduous. Cyathia in groups of three; the central male, rarely bisexual, sessile,
flowering first; the lateral bisexual, with 2–4 mm long pedicel, obscuring the male
cyathium as they develop; cymes and involucres bracteate; bracts 1.5–2 6 1–1.5 mm,
with rounded apex and fimbriate margin. Involucre campanulate, 4.5 mm across,
3.5 mm deep; cyathial glands yellow, transversely oblong, 2.5–3.5 6 1–1.5 mm;
marginal lobes with short fimbriate margin. Pedicel of male flowers 3.5 mm long;
bracteoles 3 mm long, dissected above. Pedicel of female flowers 10–14 mm long;
ovary on remarkably reflexed stalk; style arms 2 mm long, connate for 1 mm below,
bifid at apex. Capsule with 3 rounded lobes, 4 6 6–6.5 mm, on 14 mm long,
remarkably reflexed stalks. Seeds subglobose, 2.5–3 6 2–2.3 mm, grey, smooth.

Distribution. Endemic to the southwestern corner of Saudi Arabia along the

Qunfudhah–Jizan road (Fig. 5).

Habitat and flowering times. In full sun at sea level and low-lying sites (0–30 m alt.) in
fine drifting clay sand among black basalt blocks. Flowering from March to July.

Vernacular names. Saab, Suoiab.

Conservation status. Euphorbia saudiarabica has both an extent of occurrence

estimated to be less than 5000 km2 and an area of occupancy estimated to be less
than 500 km2. Moreover, the population size is estimated to number fewer than 250
mature individuals and it is known to exist at no more than three locations. The
population at one location has been severely damaged by roadworks, which have
reduced it by half. Other populations contain fewer than 30 plants, including
124 A. A. FAYED & D. A. AL-ZAHRANI

juveniles. For these reasons, it should be considered that Euphorbia saudiarabica is

an Endangered (EN) species based on the IUCN Red List Categories and Criteria,
version 3.0 and 3.1 (IUCN, 2001, 2003) under criteria B1ab (i,ii,iii,iv,v), B2ab
(i,ii,iii,iv,v), c (i,ii,iii,iv) and D. This is a precautionary preliminary assessment and
further research is needed to clarify the habitat requirements and population size of the
species. It is likely to become more threatened in the future, and additional ecological
and biological studies should be undertaken towards effective conservation.

This new species is closely related to Euphorbia parciramulosa Schweinf. However,

Euphorbia saudiarabica is readily separated by its branch margins which are almost
without undulations, while the small spine shields are non-contiguous. The spines of
the new species are small, white, black-tipped and resemble buffalo horns when
young. Moreover, the capsules are borne on long (14 mm) and remarkably reflexed
stalks (much more strongly reflexed than in Euphorbia parciramulosa). The capsules
are smooth and relatively large (4–5 6 6–6.5 mm). The glands are oblong and close
to each other. A morphological comparison between Euphorbia saudiarabica and E.
parciramulosa is given in Table 2.
Specimens examined. SAUDI ARABIA. Thahban, between Al-Birk and Al-Qahmah, 65 km N of
Shoqaiq–Muhayil junction, Al Qunfudhah–Jizan road, 4 m alt., 5 vi 1998, D. Al-Zahrani 163
(KAAU); Near Thahaban, between Qahmah and Al-Birk, Qunfudhah–Jizan road, 3 m alt., 9
v 1985, Collenette 4724 (E, K, RIY); Between Al-Birk and Al-Qahmah, Al-Qunfudhah–Jizan
road, 10 m alt., 7 viii 1997, D. Al-Zahrani 126 (E, KAAU); idem, 5 vi 1998, D. Al-Zahrani
164 (BM, E, K, M); 25 m alt., 10 xi 1998, D. Al-Zahrani 181 (KAAU); Between Baysh and
sabia-Jizan road, 35 m alt., 7 v 1985, Collenette 5195 (E, RIY); Coastal area on to Yemen
border from Abu-Arish, 8 iv 1983, Chaudhary 8106 (RIY).

T A B L E 2. Comparison of morphological characters in Euphorbia saudiarabica and E.

parciramulosa

Character E. saudiarabica E. parciramulosa

Habitat At sea level and low-lying sites On the high mountains at 2000 m alt.
at 0–30 m alt.
Habit Usually shrub to small tree, up Tree up to 6 m tall
to 3 m tall
Branches
– Colour Yellow-green to yellow Dark green
– Angles 3–5 3–4
– Margins Without undulation Undulated (with wavy edges)
Spine shields Non-contiguous Contiguous
Glands Oblong, close together Ovate to oblong-ovate, spaced
Capsule
– Size 4 6 6–6.5 mm 3–4 6 5 mm
– Pedicel 10–14 mm, totally reflexed 2–4 mm, erect to slightly reflexed
– Surface Grey, smooth Mottled
 NEW EUPHORBIA SPECIES FROM SAUDI ARABIA 125

Euphorbia taifensis Fayed & D.Al-Zahrani, sp. nov. Figs 4, 5.

Euphorbia aff. ammak Schweinf.: Collenette, Ill. Guide Fl. Saudi Arabia 237 (1985);
Collenette, Euphorbia J. 4: 102–122 (1987); Collenette, Wildfl. Saudi Arabia 307
(1999).
Arbor ramosissima succulenta spinosa usque ad 10 m alta, in omni
parte glabra, caule principali 65–90 cm in circumscriptio; rami vivide virentes

F I G . 4. Euphorbia taifensis Fayed & D.Al-Zahrani: mature plant (A) and close-up of branches
(B) at Bani Salim District, near Taif city.
126 A. A. FAYED & D. A. AL-ZAHRANI

F I G . 5. Distribution of Euphorbia madinahensis, E. saudiarabica and E. taifensis.

erecti 20–40(–50) cm in circumscriptio, 3–6(–7)-anguli, angulis acutis, spinis validis

gemellis secus cristas striatas, scutis spinarum fere contiguis. Foliorum rudimenta,
praecipue juvenilia, e rubro viridia, simplicia sessilia suborbiculata 5–5.5 mm
longa, apice mucronato, margine fimbriato, mox decidua. Cyathia terna
aggregrata, centrale masculo sessili primum florente, lateralibus bisexualibus
 NEW EUPHORBIA SPECIES FROM SAUDI ARABIA 127

pedicellatis pedicellis circa 4 mm longis, crescentibus masculum centralem

occultantibus; cymae involucraque bracteata, bracteis sessilibus suborbicularibus
vivide virentibus circa 4 6 3 mm. Involucrum poculiforme, 7–8 mm latum circa
5 mm profundum; glandulae cyathiorum flavae patentes transverse elliptico-
oblongae vel oblongo-triangulares 3.5 6 1.8 mm, lobis marginalibus margine
fimbriatis. Flores masculi pedicello 5–7 mm longo, bracteolis 3.5–4 mm longis, in
dimidio superiore dissectis. Flores feminei pedicellati, pedicello circa 1.4 cm longo,
ovario laevi, ramis stylorum circa 3 mm longis, infra connatis per 2 mm, ad apicem
bifidis. Capsula lobis 3 rotundatus, 8 6 18 mm, in stipite 14–22 mm longo, matura
vivide rubra. Semina subglobosa circa 3 mm longa grisea. – Type: Saudi Arabia:
Taif city, Bani Salim District, about 15 km SE of Taif, 1750 m alt., 18 xii 1998, D.
Al-Zahrani 198 (holo M; iso BM, CAI, E, K, KAAU, KSU, RIY).
A much branched, succulent, spiny tree, up to 10 m tall, glabrous in all parts; main
stem 65–90 cm in circumference; branches bright green, upright, 20–40(–50) cm in
circumference, 3–6(–7)-angled; angles acute, with pairs of stout spines up the fluted
ridges; spine shields almost contiguous. Leaf rudiments reddish-green especially
when young, simple, sessile, suborbicular, 5–5.5 mm long, apex mucronate, margin
fimbriate, soon deciduous. Cyathia in groups of three; the central male, sessile,
flowering first; the lateral bisexual, pedicellate, pedicel c.4 mm long, obscuring the
male cyathium as they develop; cymes and involucres bracteate; bracts sessile,
suborbicular, bright green, c.4 6 3 mm. Involucre cup-shaped, 7–8 mm across,
c.5 mm deep; cyathial glands yellow, patent, transversely elliptic-oblong to oblong-
triangular, 3.5 6 1.8 mm; marginal lobes with fimbriate margin. Pedicel of male
flowers 5–7 mm long; bracteoles 3.5–4 mm long, dissected in the upper half. Pedicel
of female flower stout, c.14 mm long; ovary smooth; style arms c.3 mm long, connate
for 2 mm below, bifid at apex. Capsule with 3 rounded lobes, 8 6 18 mm on 14–
22 mm long stalk, ripening bright red. Seeds subglobose, c.3 mm long, grey.

Distribution. Euphorbia taifensis is named after Taif city where the species is endemic
(Fig. 5).

Habitat and flowering times. The plants are very localized, occurring on the stony
and rocky slopes of wadis and near farms at elevations ranging between 1700 and
2100 m. The new species is well established and occurs in large colonies with good
regeneration. Flowering and fruiting from October to February.

Vernacular names. Amaq, Amaqah, Amaqat al-ghanam.

Conservation status. The new species has both an extent of occurrence of less than
20,000 km2 and an area of occupancy of less than 2000 km2. It is known to exist at no
more than 10 locations and continuing decline has been observed. It is therefore to
be considered as Vulnerable (VU) under criteria B1ab (i,ii,iv,v) + 2ab (i,ii,iv,v)
according to the IUCN Red List Categories and Criteria, version 3.0 and 3.1 (IUCN,
2001, 2003).
128 A. A. FAYED & D. A. AL-ZAHRANI

T A B L E 3. Comparison of morphological characters in Euphorbia taifensis and E. ammak

Character E. taifensis E. ammak

Habit Up to 10 m tall Up to 6 m tall
Leaf
– Colour Reddish-green Green
– Size 5 6 5.5 mm 6 6 10–20(30) mm
– Apex Mucronate Acute
– Margin Fimbriate Entire
Capsule
– Size 8 6 18 mm 7–10 6 12(–14) mm
– Shape Triangular, rounded Triangular, acute
– Pedicel 14–22 mm 9–11 mm

This new species is similar in its growth form and involucral characters to Euphorbia
ammak Schweinf. However, Euphorbia taifensis is easily distinguished through its
leaf characters: reddish-green, 5–5.5 mm long, suborbicular, with mucronate apex
and fimbriate margins. In addition our species is taller (attaining 10 m). Moreover, the
capsule lobes are rounded and the inflorescence size is quite different. A morphological
comparison between Euphorbia taifensis and E. ammak is given in Table 3.
Specimens examined. SAUDI ARABIA. Thaqif, Sakharah village, 9 vii 1946, Vesy-FitzGerald
16560 (BM); Near Haritha, Wadi Wahht, SW of Taif, 2170 m alt., 21 xi 1986, Collenette 5928
(E, RIY); Taif, Bani Salim District, 15 km SE of Taif, 1750 m alt., 18 xii 1998, D. Al-Zahrani
198 (BM, CAI, E, K, KAAU, KSU, M, RIY); Taif, Bani Salim District, 15 km SE of Taif,
1750 m alt., 25 xii 1998, D. Al-Zahrani 199 (KAAU); Jebal Amudh, by wadi Aoff wadi Wijj,
18 km from Taif, 2000 m alt., 9 iv 1978, Collenette 627 (K); Taif, wadi Sakarah, between
Misan and Al-Baha, 28 xi 1992, Collenette 8433 [spirit sample no. 62829 (K)]; Wadi Sakarah, 4
iii 1993, Collenette 7940 [spirit sample no. 57329 (K)].

A CKNOWLEDGEMENTS
We are greatly indebted to the directors and members of staff of the herbaria at the
Royal Botanic Gardens, Kew, Royal Botanic Garden Edinburgh, and British
Museum (Natural History) for the facilities provided, valuable discussions and
useful comments. Thanks are also due to the authorities of the Faculty of Science,
King Abdulaziz University in Jeddah, Faculty of Science, King Saud University in
Riyadh, and the National Herbarium in Riyadh for offering facilities to conduct this
work. We would also like to thank two anonymous referees for their valuable
comments and for useful discussions.

R EFERENCES
C O L L E N E T T E , S . (1985). An Illustrated Guide to the Flowers of Saudi Arabia. London:
Scorpion Publishing.
C O L L E N E T T E , S . (1987). Spiny Euphorbias in Arabia. Euphorbia J. 4: 102–122.
 NEW EUPHORBIA SPECIES FROM SAUDI ARABIA 129

C O L L E N E T T E , S. (1999). Wildflowers of Saudi Arabia. NCWCD, Kingdom of Saudi Arabia.

I U C N (2001). IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival
Commission. Gland, Switzerland and Cambridge, UK: IUCN.
I U C N (2003). Guidelines for Using the IUCN Red List Categories and Criteria: Version 3.0.
IUCN Species Survival Commission. Gland, Switzerland and Cambridge, UK: IUCN.

Received 2 September 2006; accepted for publication 12 February 2007