ligule origins

[John Grehan]

The structural and functional description by Robert Haynes
says nothing directly about the evolutionary significance of
the ligule. A Creationist could have provided the same
description. The presumption that function of a sturcture
(whether current function or former function) is its ultimate
cause seems to me to be a matter of faith than emprical
reality.

So I would agree with Janzen's inference that the time of origin
does not put consideration of their original adaptive value
effectively out of reach since its not a matter of time of
origin, but rather one of philosophical perspective (my
opinion on which most will disagree I expect).

Croiat (1960) in his Principia Botanica identifies the
ligule of Selaginella as one of many morphological
manifestations of trichomoids - left over remnants of
ancestral structures. He places trichomoids as being
neither telome or phyllome, but an enation barely
higher than a trichome and evolutionarily capable of developing
into a leaf or shoot. Croizat suggests that a lack of
broad understanding of trichomoids leads to
misconceptions about the individual morphological
variants that include ligules, stipules, jiggers,
kolleteren, axillarschuppen etc.

John Grehan