The species of Ephedra are found distributed in North as well as in South America, Spain, France, the Mediterranean regions, and India. It is interesting to note that, not a single species has yet been recorded, which is common to both the Hemispheres.
According to Hooker, there are three species of Ephedra growing in India:
i. E. vulgaris,
ii. E. pachyclada, and
iii. E. peduncularis.
From Ephedra a valuable alkaloid ‘ephedrine’ is extracted, which is extensively used in bronchial troubles.
The Sporophyte of Ephedra:
Plants are low-growing shrubs, while a few are woody climbers, or prostrate. In some places they serve as sand-binders. The plant is highly xeromorphic, and grows on rocks or in sandy places. The leaves are rudimentary, and practically of no importance to the plant, as the stem itself is ribbed phylloclade.
They are usually decussately arranged, but may occur in whorls of three, very rarely of four. They are connate at their bases forming a small sheath. The branches appear in two’s or three’s from the axillary buds, and may fall off in some species at the end of the growing season, and are replaced by new ones in the next season; such species may be regarded as deciduous ones, by analogizing them with trees shedding off their leaves in winter. Internally, the stem has got a conspicuously thick epidermis, and groups of sclerenchyma cells occur below each rib.
Sunken stomata occur in the furrows. The cortex is loose in texture, and differentiated into an outer palisade and inner spongy tissues, the cells of both of which contain abundant chloroplasts.
Below the cortex there is an endodermal layer, encircling an endarch, siphonostelic vascular cylinder, the bundles of which are conjoint, collateral, and open. The tracheids are provided either with single or alternating double rows of bordered pits, with Bars of Sanio and trabeculae.
In young stems, the medullary rays are uniseriate. At or near about the nodes, the cells of the pith get highly lignified, and form transverse plates. Resin canals are entirely absent, but cells containing large, stellate, calcium oxalate crystals are frequently met with.
A group of thick-walled cells with dense cell-contents (most probably tannin) occur in the centre of the pith. The stem grows in girth due to secondary growth, and prominent annual rings are formed. The secondary wood possesses vessels in addition to tracheids.
Ephedra is dioecious. It is interesting to note, however, that though normally male and female strobili are borne on different individuals, yet monoecious plants are not rare in nature, e.g., E. foliata. Furthermore, bisporangiate flowers may be found in species like E. camphylopoda, E. trifurca, etc.
Staminate (or Male) Strobilus:
Staminate strobili occur in groups of two, three or four, from the nodes of the branches. Each strobilus is a compound one, appears in the axil of a leaf, and consists of a short axis, bearing 2-8 decussately arranged bracts; the lower 1-2 pairs of bracts are usually sterile, while each of the rest bears a single male flower.
Each male flower is represented by a single stamen, having a stalk bearing a variable number of microsporangia (or anthers) at its tip, subtended at the base by a pair of delicate, oppositely placed scales, which coalesce together forming a structure that has been doubtfully interpreted as a perianth.
The stalk bearing the microsporangia has been referred to by some as sporangiophore or antherophore. Each microsporangium is 2-3 lobed, and the lobes open by apical slit. The microspore mother cells (or pollen mother cells) inside the microsporangium, on undergoing reduction division give rise to microspores or pollen grains.
Pistillate (or Female) Strobilus:
The mode of distribution of the female strobili is practically the same as that of the male ones, and their structures are also very similar. The former ones are, however, rather shorter and more pointed, than the latter.
Each strobilus consists of a few pairs (usually 4) of sterile bracts, and either a solitary ovule or 2-3 of them. The bracts may be fleshy or dry, and winged, and sometimes highly coloured for the purpose of effective dispersal by animals or wind, as the case may be.
The structure of the ovule is fundamentally the same as in other gymnosperms. There is the nucellus surrounded by two integuments, the outer one being formed by four segments (bracts), coalescent at the base, and the inner integument is formed of two such coalescent bracts.
The upper portion of the nucellus is separate from the inner integument, which, at the time of pollination, prolongs out considerably, giving rise to a smooth or spirally coiled micropylar tube. The pollination drop is exuded at the tip of this micropylar tube. At the tip of the nucellus there is a conspicuously deep pollen chamber, whose bottom actually touches the apex of the female gametophyte (endosperm).
The Gametophytes of Ephedra:
Male Gametophyte:
The microspore or pollen grain is the first cell of the male gametophyte. The mode of development in this case follows the plan as found in Pinus. It is to be noted, however, that the prothallial nucleus, formed as a result of the second division, is not separated from the rest (antheridial initial) of the developing gametophyte by means of a wall.
The antheridial initial divides to form a tube cell, and a generative cell, the latter dividing in its turn and giving rise to two nuclei, a stalk cell nucleus and a body cell nucleus; these two nuclei invariably lie enclosed within a common cytoplasmic envelope, and there is no formation of a cell wall in between the two.
The pollen grains are liberated at this stage. Before the shedding, however, the two prothallial cells get completely disorganized. Pollination is effected sometimes in early March. On reaching the ovule, the body cell divides, and forms two identical male gamete nuclei. Finally, the exine bursts open, and the intine pushes itself out into a short pollen tube.
Female Gametophyte:
The megaspore is the first cell of the female gametophyte. As in all other gymnosperms, the functional megaspore develops from the lowest of a linear tetrad of megaspores, and undergoes a period of free nuclear division. At the 256 nuclear stage, cell walls begin to be laid down rapidly in a centripetal fashion, and finally the female gametophyte (endosperm) becomes entirely cellular.
Even before the female gametophyte is cellular throughout; a differentiation takes place inside it forming two regions, an upper reproductive one composed of large elongated cells, and a lower nutritive one made up of comparatively much smaller cells.
Finally, the lower nutritive region gets further differentiation into an upper tissue performing the function of reservoir of food, and a lower mass of cells constituting a haustorium, which absorbs nutrients from the nucellus.
At the micropylar end of the endosperm, archegonia develop, usually two in number; occasionally, there is only one archegonium, and rarely there are three. The number of neck cells are rather heavy in Ephedra, and stands at 32 or more. There is no wall formed in between the ventral canal nucleus and the egg nucleus.
The time interval in between pollination and fertilization is exceptionally short for a gymnosperm, and is less than a period of 12 hours. The short pollen tube pierces through the neck of the archegonium, and by the bursting of its tip, the contents are discharged in the egg.
The first male gamete nucleus actually unites with the egg nucleus forming oospore, while the second male gamete nucleus and the ventral canal nucleus undergo divisions producing the nuclei for a few, minute, very short-lived cells at the top of the oospore.
But this tissue is considered, by some workers, as equivalent to the endosperm of the angiosperms, at least physiologically, as it is readily absorbed by the developing embryo. On the other hand, Herzfeld describes the fusion of the second male gamete nucleus with the ventral canal nucleus, and calls it a case of double fertilization as found in the angiosperms.
The New Sporophyte of Ephedra:
The oospore nucleus divides freely, and usually forms eight nuclei, which remain more or less evenly distributed throughout the cytoplasm. Each of these nuclei is organized into a cell, and can be regarded as a potential young embryo; this is an instance of polyembryony, where no cleavage takes place.
Normally, 3-5 of these embryos begin further development. At first, the embryo cell nucleus divides into two unequal parts without any corresponding cell-wall formation. A small tubular outgrowth is developed, and the larger nucleus passes into it moving towards the tip, behind this, a transverse wall is formed.
The terminal cell, thus cut off, divides and forms the pro-embryo, from the tip of which the embryo is developed. The remaining portion of the tube with its nucleus forms the suspensor which elongates subsequently and helps in pushing the developing sporophyte (embryo) down within the nutritive tissue.
The cells of the pro-embryo lying behind the tip also elongate to some extent, and form the secondary suspensor. Only one embryo, however, usually reaches maturity. The seed is dicotyledonous with two linear cotyledons, and the mode of germination is hypogeal. On germination the seed gives rise to a seedling sporophyte.
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