Lycophyta: clubmosses and quillworts
I. New advances which evolved in the lycophyte line include:
a. Microphyll - a true leaf with a single vein whose trace is not associated with a leaf gap.
Although genera that still exist have small microphylls, species of the past had rather 'macro-sized' microphylls which could extend several feet in length. The micro connotation comes from fact that only 1 vein serves the leaf, not that the leaf itself is small.
b. True Root - which allows the support of a larger mass as enables better absorption of water containing nutrients and can help balance the larger leaf mass above.
c. We see the evolution of Heterospory, in which two spores types are formed.. one for the production of an egg-bearing, and another for a male gamete producing plant. This way the possibility of self-fertilization could not occur.
d. Evolution of 950+ species, the survivors of which generally look more like mosses, than their noble ancestors of the pastLycopodium - ground pines 50 sp
Selaginella - spike mosses 700 sp
Isoetes - quillwort 60 sp
II. Lycopodium: whose characteristics include:
- true roots,
- microphylls ( true leaves) and
- a strobilus which houses spores ( though at this point only homospory- one type of spore).
Each spore may germinate into a 1N gametophyte which can take 6-15 years to mature. Dependent on the species, some of the gametophytes will grow on the surface of the ground and photosynthesize, while others grow below ground in a symbiotic relationship which helps support their growth.The gametophyte produces both antheridiums and archegonia when mature.
Fertilization of the egg results in a zygote which then grows into the large sporophyte. shown above