AskDefine | Define microphyll

User Contributed Dictionary

English

Etymology

From micro- (small) + "phyll" (leaf)

Noun

  1. In the context of "Botany": A leaf having a single unbranched vein, or a structure that is derived from such a leaf.

Antonyms

See also

Extensive Definition

The "Enation theory" of microphyll development posits that small outgrowth, or enations, developed from the side of early axes (such as those found in the Zosterophylls) . Outgrowths of the protostele later emerged towards the enations (as in Asteroxylon), Even some conifer needles bear only a single vascular trace, but again, this evolved as a secondary simplification from a multi-veined leaf.
We have problems in the other direction, too. The lycopods are the only clade accepted to have evolved microphylls de novo, instead of by reduction from a megaphyll, but even they throw up exceptions: some Selaginella species have a complex venation instead of microphylls.
To make matters worse, there is also some debate about whether leaf gaps are unique and/or common to megaphyllous organisms.
This ambiguity leaves it difficult to distinguish between two competing hypotheses: that microphylls evolved via the reduction of megaphylls, and that they evolved independently, from enations. Taxonomically, the terms are perhaps better left undistinguished until more is known of their origins - perhaps the term "leaf" is more appropriate.

References

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