मुख्य रूप से उष्णकटिबंधीय या जेरोफेटिक वुडी पौधे; व्यावहारिक रूप से जीवाश्म के रूप में अज्ञात लेकिन एंजियोस्पर्म की पैतृक रेखा के करीब माना जाता है

gnetales's Usage Examples:

17, C, a); he suggests they may represent vestigial structures pointing back to some ancestral form beyond the limits of the present group. The Gnetales probably had a separate origin from the other Gymnosperms; they carry us nearer to the Angiosperms, but we have as yet no satisfactory evidence that they represent a stage in the direct line of Angiospermic evolution.

The genus Ephedra, with its prothallus and archegonia, which are similar to those of other Gymnosperms, may be safely regarded as the most primitive of the Gnetales.

In the more heterogeneous structure of the wood and in the possession of true vessels the Gnetales agree closely with the higher flowering plants.

Our knowledge of the Gnetales leaves much to be desired, but such facts as we possess would seem to indicate that this group is of special importance as foreshadowing, more than any other Gymnosperms, the Angiospermous type.

The three existing genera, usually spoken of as members of the Gnetales, differ from one another more than is consistent with their inclusion in a single family; we may therefore better express their diverse characters by regarding them as types of three separate families-0) Ephedroideae, genus Ephedra; (2) Welwitschioideae, genus Welwitschia; (3) Gnetoideae, genus Gnetum.

Gnetales.

Secondary xylem and phloem produced by a single cambium, or by successive cambial zones; no true vessels (except in the Gnetales) in the wood, and no companioncells in the phloem.

Flowers unisexual, except in a few cases (Gnetales) without a perianth.

Although there are several morphological features in the three genera of Gnetales which might seem to bring them into line with the Angiosperms, it is usual to regard these resemblances as parallel developments along distinct lines rather than to interpret them as evidence of direct relationship.

The Gnetales are a class apart, including three living genera, of which we know next to nothing as regards their past history or line of descent.

gnetales's Meaning':

chiefly tropical or xerophytic woody plants; practically unknown as fossils but considered close to the ancestral line of angiosperms