Gnetales:

Foster and Gifford (1959) described Gnetales as “a small group of gymnosperm-like plants”
while Maheshwari and Vasil (1961) Mentioned that ” the order Gnetales, formerly included
three genera, Ephedra, Welwitschia and Gnetum which were considered to be highest evolved
among the gymnosperms and believed to show an approach to the angiosperms”.

But mainly due to the presence of naked ovules and also because of the absence of true style
and stigma in Ephedra, Welwitschia and Gnetum, these members can only be treated under
gymnosperms and not under angiosperms.

General Characteristics of Gnetales:

Gnetales, believed by some botanists to be the ancestors of flowering plants

or angiosperms, are the highly evolved members of gymnosperms and
show following characteristics:

1. These are woody plants, of which some species are trees (Gnetum gnemon), many are
lianes or shrubs and a few are stumpy turnip-like (e.g. Welwitschia mirabilis).

2. Leaves are simple elliptical or strap-shaped or sometimes reduced to minute scales. They
are generally opposite or whorled.

3. Vessels are present in the secondary wood.

4. „Flowers‟ are unisexual, usually dioecious and only rarely monoecious as in some species
of Gnetum.

5. ‘Flowers’ are arranged in compound strobili or „inflorescences‟.

6. The male flowers are surrounded by a perianth. Each male flower contains an antherophore
with one to eight synangia.

7. A single erect orthotropous ovule is present in each female flower.

8. Nucellus of the ovule remains surrounded by two or three envelopes.

9. The micropyle of each ovule remains projected in the form of a long bristle-like tube.

10. At the time of fertilization the pollen tube contains two male nuclei.

11. A unicellular primary suspensor is present in the embryo.

12. Two cotyledons are present in the embryo.

Classification of Gnetales:

Sporne (1965) divided Gnetales into following three unigeneric

families:
(i) Gnetaceae: Gnetum

(ii) Ephedraceae: Ephedra

(iii) Welwitschiaceae: Welwitschia

Distribution of Ephedra:

Ephedra (commonly known as joint pine, joint fir, Mormon tea or Brigham tea) is the only
genus in family Ephedraceae and order Ephedrales. It is represented by 50 species.

These species grow in dry climate over wide areas of the Northern hemisphere including
North America,Europe, North Africa, and South west and central Asia. Eight species of
Ephedra are known from India. Some of the common Indian species are E. intermedia, E.
gerardiana, E. sexatilis, E.foliata etc. These species are distributed in dry parts of Punjab,
Haryana, Rajasthan and parts of Kashmir to Sikkim.

Morphological Features of Ephedra:

The plant body is sporophytic and shows xerophytic characters. Mostly the plants are woody
shrubs (Fig. 1 A), a very few species are lianas and some species grow into a small tree. E.
compacta reaches 30 cm in height E. triandra is a tree. Its height is several meters. Plant body
can be differentiated into three parts – root, stem and leaves.

1. Root:

There is a prominent underground tap root system. Later on the adventitious roots develop.
Many root hairs are present but there is no mycorrhiza.

2. Stem:

Like Equisetum, the stem is green, ribbed, branched, fluted and differentiated into nodes and
internodes (Fig.1B). It is distinctly jointed fir) (therefore, commonly known as jointed fir). It
performs the function of photosynthesis and may be called as phylloclade. The branches arise
from the axillary buds and are, therefore, in pairs of threes or fours according to the number
of the scaly leaves at the nodes in different species.

The branches are also green and differentiated into nodes and internodes. The branching
starts early at the cotyledonary stage. The apical meristem is having well marked tunica layer
but the growth of internode is independent due to the presence of the meristemetic zone at its
base. This zone dries up at the end of each growing season. It results in the brittleness and
shedding of the branches. These branches are again replaced in next season by new axillary
branches.

3. Leaves:

Leaves are small scaly, present in pairs at the nodes and are arranged in opposite decussate
manner. (Fig. 1 C, D). These leaves unite at the base to form a basal sheath. Each leaf
contains two unbranched, parallel veins. They are so minute that they are of no use i. e.,
unable to perform photosynthesis. The function of photosynthesis is carried by green stem. In
the axil of each leaf is present a bud for the branch. True foliage leaves are absent.

Internal Structures of Ephedra:

1. Stem:

The stem is ribbed; so, in transverse section stem shows ridges and grooves (Fig. 2A).

A T.S. of stem at node shows the following structures (Fig. 2A, B):
a. Epidermis: It is the outermost layer of thick walled cells, covered with a thick layer of
cuticle. Sunken stomata are present on the slopes of the ridges in the circular pits.

b. Hypodermis: It is present just below the ridges. (Fig 2B). It is made up of

sclerenchymatous cells and provides mechanical strength to the plant.

c. Cortex: In is present between the thick walled sclerenchyma and vascular cylinder. It can
be differentiated into outer and inner cortex. The outer cortex contains 2-3 layers of radially
elongated palisade tissue and inner cortex consists of 2-3 layers of spongy parenchyma.

The cells of outer and inner cortex are loosely arranged with large intercellular spaces and are
provided with chlorophyll to perform the function of photosynthesis. A few patches of
scleranchymatous cells may also occur in the cortex to provide mechanical support to the
young axis.

d. Endodermis: It is the innermost layer of cortex. It is not easily distinguishable from the
cortical cells.
e. Pericycle: It is present below the
endodermis. It is single layered and ill
defined.

f. Vascular Cylinder: It is endarch, and

consists of many vascular bundles
arranged in a ring. Vascular bundles are
conjointed, collateral, open and endarch.
The number of primary vascular strands is
generally eight, out of which four small
represent the foliar traces while the other
large four are stem bundles.

Foliar traces run upto the node. Xylem

consists of tracheids, vessels and xylem
parenchyma. Due to the presence of the Secondary growth:
vessels the Ephedra resembles
angiosperms. The phloem consists of sieve The secondary growth takes place by the
cells, phloem parenchyma and albuminous activity of intrafascicular cambium and
cells. Phloem and xylem are separated by a interfascicular cambium. After forming a
narrow strip of cambium. complete ring of cambium, the cambial
cells cut of secondary phloem on the outer
g. Medullary rays: side and secondary xylem towards the
Broad, parenchymatous medullary rays are inner side. (Fig. 4)
present in between the vascular bundles. Due to formation of the secondary tissues,
Medullary rays connect the pith with primary phloem is crushed and the primary
cortex. xylem is pushed towards the inner side at
It is present in the centre. It is made up off the base of the secondary xylem. In
thin walled parenchymatous cells. Near the addition to vascular tissue cambium also
node its cells become strongly lignified forms medullary rays (secondary). These
forming a peridermal diaphragm which rays are long, broad (multiseriate) and
accounts for the rapid separation of the traverse between secondary xylem and
branches in the region (Fig. 3). secondary phloem.
 Tangential Longitudinal Section
(T.L.S.) of wood:

Like R.L.S. in T.L.S. also, the xylem,

tracheids, vessels and medullary rays are
clearly visible but they are cut transversely
here. (Fig. 6). Bordered pits and simple
pits are seen on the radial and tangential
walls. The medullary rays are elongated
and on their tangential walls are present
simple pits.

Radial Longitudinal Section (R.L.S.):

In R.L.S. xylem tracheids, vessels and

medullary rays are clearly visible.
Medullary rays are cut lengthwise and
their length and height are revealed (Fig.
5A). Each medullary ray is composed of
irregularly dispersed ray cells and ray
tracheids. Tracheids possess bordered pits
on their radial and tangential walls. In
vessels, the bordered pits are also arranged
in the same way as tracheids (Fig. 5 B, C).
2. Leaf: 3. Root:

The transverse section of scaly leaf is oval The transverse section of root shows single
in shape and can be differentiated into layer epiblema, outer cortex (composed of
epidermis, mesophyll tissue and vascular collenchymatous cells), inner cortex
tissue. (composed of parenchymatous cells)
endodermis and pericycle. Vascular
a. Epidermis: bundles are radial and exarch. The root
It is outer most single layer of thick walled may be diarch or triarch.
elongated cells. The cells are covered with
thick cuticle. Sunken stomata are present
(Fig. 7). Reproduction in Ephedra:

Ephedra is heterosporous (produces two

types of spores: microspores and
macrospores) and dioecious (both these
types of spores are produced on two
different plants of the same species. E.
fuliata is monoecious. Microspores are
formed in male flowers while megaspores
are formed in female flowers.

These flowers are present in the form of

cone like compound strobili. Male flowers
are present in the form of male strobilus
while female flowers are present in the
form of female strobilus. Both male and
female strobili are compound i. e.,the cone
axis bears pairs of bracts which subtend
either microsproangiate or ovulate shoots.
b. Mesophyll tissue: Male Strobilus (Staminate Strobilus):
Two or three layers of palisade tissue are Male strobili arise in clusters from the
present inner to epidermis. The cells are nodes of the branches. Each strobilus is
filled with chloroplast and large rounded, ovoid or spherical in shape and
intercellular spaces are present between arises in the axis of a scale leaf. Their
them. In the centre of the leaf number at the node depends upon the
parenchymatous tissue is present. number of scale leaves.
c. Vascular tissue: Each strobilus has a central axis which
bears 2-12 pairs decussately arranged
Two vascular bundles are embedded in the
simple, broad and cupped bracts. Lower
parenchymatous tissue. The vascular
most 1-2 pairs of bracts are sterile. In the
bundles are collateral and closed. Xylem is
axil of each fertile bract arises a male
present towards the upper side.
flower or staminate flower (Fig. 8 A-C). A
male strobilus with several male flowers Structure of microsporangium:
can be compared with an inflorescence.
Each microsporangium has 2-3 loculi and
is often called as synangium. Its wall is
two layered followed by a prominent
tapetal layer enclosing a sporangial sac
having many pollen grains or microspores
(Fig. 8E).

Development of microsporangium:

The development of microsporangium is

eusporangiate. Microspangia arise at the
tip of microsporangiophore. The
microsporangiophore arises as small
protuberance in the axil of the fertile bract
of male strobilus. The apex of
microsporangiophore becomes lobed after
growing for some time.

Each lobe represents a sporangium. Few

hypodermal cells in each lobe enlarge in
size. These cells consist large nuclei,
denser cytoplasts and are known as
archesporial cells. These cells divide
periclinally into outer primary wall cells or
primary parietal cells and primary
sporogenous cells (Fig. 9A).

Primary sporogenous cells further divide

by two periclinal divisions to differentiate
middle wall layer, inner tapetal layer and
Male flowers: sporogenous cells. The primary wall cells
function directly as the outer wall of the
Each male flower has two lipped thin
sporangium.
bractioles (perianth) which encloses a
stamen. Bracteoles are united at the base. However, according to some workers, the
The flower has a short stalk known as primary wall cells divide periclinally to
microsporangiophore and two, eight to form three layered thick wall. The
twelve microsporangia at its tip (Fig. 8 D). sporogenous cells divide further to form
large number of microspore mother cells.
Microsporangia are sessile and dehisce
Each microspore mother cell divides by
terminally. Male flower is also called
meiosis to form four haploid microspores
simple strobilus. A compound male
arranged in a linear tetrad.
strobilus, therefore, consists of many such
strobili.
 Female Strobilus (Ovulate Strobilus) or
Female Cone:

They usually arise in pairs at each node in

the axil of scale leaves. A female strobilus
appears to be an elliptical structure with a
pointed apex (Fig. 11 A, B). It retains the
same compound structure as the male
strobilus. It consists of a short axis to
which are attached three or four pairs of
decussate bracts.

In E. Americana these bracts are swollen

and juicy (Fig. 11E). All the pairs of bracts
are sterile except the uppermost one which
bears a pair of ovules in its axil (Fig. 11C,
D) and may be variously coloured. Out of
the pairs of the ovules only one survives
and it takes up a false terminal position.

Structure of pollen grain:

Pollen grain is the first cell of the male

gametophyte. Each pollen grain is
elliptical, uninucleate and has two wall
layers. The outer wall layer is thick and is
called exine while the inner male layer is
then and is called intine (Fig. 10A, B).
Female flower:

The female flower has short stalk and an

ovule (megasporangium)

Structure of ovule (megasporangium):

Longitudinal section of an ovule shows

that it consists of a mass of
parenchymatous cells in the centre. It is
called nucellus. The nucellus is surrounded
by a two-layered envelope. These are
usually designated as outer and inner
integuments. The outer envelope is formed
by four segments and receives four
bundles while the inner one is formed of
two segments and receives two bundles.

The lower half of the inner envelope is

fused to the nucellus but upper half is free
and prolongs into a long micropyle tube.
By the time of pollination just below the
micropyle pollen chamber develops.
Pollen chamber in Ephedra is the deepest
known among the Gymnosperms. The
floor of the pollen chamber is formed by
female gametophytic tissue and not by the
nucellus as in other gymnosperms. (Fig.
12).

Development of Ovule:

Development of the ovule takes place in

the form of a small cellular protuberance. The megaspore mother cell divides
This protuberance increases in size and meiotically to form four hapliod
becomes the nucellus. Soon neighbouring megaspores. Generally the lowermost
cells of the base forms inner and outer megaspore (towards the chalazal end)
integuments. Inner integument surrounds remains functional. It enlarges and gives
the nucellus except the top where it form a rise to female gametophyte (first cell of the
small opening called micropyle. female gametophyte) and the remaining
upper three megaspores degenerate.
A hypodermal archesporial cell
differentiates in the nucellus. It divides Gametophytic Phase:
periclinally into outer parietal cell and The sporogenesis results in the formation
inner megaspore mother cell. The latter is of micro- and megaspores representing the
pushed quite deep into the nucellar tissue. gametophytic stage. They undergo
gametogenesis to form the male and
female gametophytes respectively.
Development of female gametophyte:
Development of male gametophyte
As mentioned earlier, the functional
before pollination:
megaspore is the first cell of the female
It takes place in microsporangium. After gametophyte. It enlarges and its nucleus
the reduction division spores tetrads are divides into two. These nuclei move
formed. The four cells of the tetrad towards the opposite pole and are
separate and develop into microspores. separated by a large central vacuole.
The microspore divides by a transverse
wall to form a small prothallial cell and a Later these two nuclei divide by free
large outer cell is (Fig. 13 A). The outer nuclear division to form as many as 256
cell again divides by a transverse wall and nuclei. These nuclei are arranged in a
forms a second prothallial cell and an peripheral layer around the central
antheridial cell. (Fig 13 B). vacuole. Later the central vacuole
disappears and free nuclei are evenly
The antheridial cell divides to form a small distributed throughout.
generative cell and a large tube cell (Fig.
13 C, D). The generative cell soon divides Centripetal wall formation (from periphery
into the nuclei of stalk cell and body cell. towards the centre) starts and thus a mass
The nuclei of stalk cell and body cell of cellular tissue is formed. It is called
remain surrounded by a common mass of female gametophyte or endosperm.
cytoplasm (Fig. 13 E, F). Pollens are shed Gradually the female gametophyte is
at this five celled stage. differentiated into two regions.

Micropylar region and antipodal region.

Micropylar region consists of loosely
arranged thin walled cells, which later on
give rise to archegonia. Antipodal region is
further differentiated into lower storage
zone and basal haustorial zone. Storage
zone comprises of bulk of endosperm. This
zone consists of compactly arranged cells
which are full of starch and other food.
The cells of the haustorial zone absorb the
food material from the nucellus.

Structure and development of

archegonium:

Archegonia arise in the micropylar region.

The number of archegonia in Ephedra
varies from 1-3 but they are generally two
in number. Any superficial cell of female
gametophyte towards micropylar region
acts as archegonial initial (Fig. 14A). It The neck of archegonium of Ephedra is the
divides by a transverse division to form longest in the gymnosperms. The central
outer primary neck cell or neck initial and cell enlarges in size. Its nucleus divides
inner central cell (Fig. 14B). The neck cell into a ventral canal nucleus and an egg
undergoes a number of divisions to form a nucleus but no wall is laid down between
long neck of 8 or more tiers (minimum of the two.
32 cells). It encloses no neck canal.
As the archegonium reaches towards
maturity, the cells of neck usually merge
with surrounding gametophytic cells and
become undistinguishable from the
surrounding cells of female gametophyte.
The cells adjacent to the central cell divide
transversely to form a distinct jacket layer,
which may be two or three layer thick.

A mature archegonium consists of a long

neck and a central cell having a ventral
canal nucleus and egg nucleus (Fig. 13,
14).

Pollination:

The pollination is anemophilous i.e. it

takes place by wind. Pollen grains are
carried by the wind on the female
strobilus. The cells of the nucellus secrete
pollination drop which comes out through
the micropylar canal. Pollen grains to
adhere to the pollination drop. Pollen
grains are sucked inside and come to lie in
a deep pollen chamber.

Development of male gametophyte after

pollination:

Pollen grains germinate in the pollen

chamber. The exine ruptures and intine
comes out in the form of pollen tube. The
nucleus of the body cell divides to form
two male gametes (Fig. 16)
 Embryogeny:

More than one archegonium may be

fertilized in an ovule, but only one oospore
develops into embryo. The zygote nucleus
divides by three free nuclear divisions to
form eight nuclei. These nuclei are
irregularly distributed in the cytoplasm of
the archegonium.

Later wall-formation takes place and this

structure is known as proembryo. Each cell
of inproembryo is capable to develop into
Fertilization: an independent embryo. Three to five of
these nuclei individually enclose in
It occurs 10 hours after pollination. The somewhat irregular walls and become
pollen tube along with its four nuclei (2 globular.
male nuclei, 1 stalk nucleus and 1 tube
nucleus) gradually penetrates the neck cell These are known as pro-embryonal cells,
of the archegonium and discharges all the each of which produces an independent
four nuclei into the egg. embryo. In Ephedra, this type of
polyembrony without any cleavage, it
One male nucleus fuses with the egg unique among gymnosperms. Because the
nucleus forming the zygote (2x) or polyembryony occurs without any
oopsore. Khan (1941) observed in E.foliata cleavage, it is known as embryo sac
that second male gamete fuses with the polyembryony. Each proembryo grows
ventral canal nucleus (double fertilization) into tubular structure called the suspensor
but this diploid nucleus does not develop (Fig. 18A-C).
into embryo Oospore is the first cell of the
sporophytic phase (Fig. 17). Tube nucleus of the proembryo divides
into two. Both these nuclei move into the
tube. A wall separates these two daughter
nuclei and forms two cell(Fig. 18D). The
cell towards the micropylar and
disintegrates while the cell formed towards
the chalazal end of the tube survives and is
called embryonal initial.

The tube grows more and carries the

embryonal initial deep into theprothallus
tissue. This embryonal initial divides into a
proximal suspensor cell and a
distalembryo cell. The embryo cell divides
and develops into the embryo proper
which contains two cotyledons (Fig. 18E-
G).Although several embryos may develop Structure of Seed:
in a single ovule but only one survives and
reaches at maturity as seed. Longitudinal section of the seed shows
that it consists of a dicotyledonous embryo
in the centre. This embryo is situated at the
tip of the elongated suspensor and remains
embedded in the endosperm (Fig. 19). The
nucellus is consumed during the
development of embryo and persists as a
nucellar cap at the micropylar end of the
seed.

The seed is enclosed by the seed coat

which consists of two separate layers
derived from the two envelopes. At the
time of maturity, the subtending bracts of
the megasporangiate strobilus become
thick and fleshy and form an additional
covering around the seed e.g., E. foliata.

Germination of the seed:

Seeds germinate without undergoing a period of rest if the atmospheric conditions are
favourable. The seed germination is epigeal (Fig. 20A-G).
Economic Importance of Ephedra:

1. An alkaloid ephedrine is obtained from E. gerardiana, E. intermedia, E. nebrodensis etc. It

is used in preparation of medicines that cure cough, bronchitis, asthma and hay fever.

2. Tincture of E. gerardiana is also used as a cardiac and circulatory stimulant.

3. Decoction of the stem and roots is used to cure rheumatism and syphilis e.g.,E.
antisyphilitica.

4. The juice of berry is used to cure respiratory disorders.

5. Mormon tea is brewed from the species of Ephedra in south western United States.

6. Some species are grown as ornamentals.