Domain Eucarya
Kingdom Plantae
Subkingdom Spermatophyta
Division Gnetophyta
Missing links, or just plain weird?
A division/phylum of bizarre-looking plants in 3 genera that baffled botanists for years, until they decided they were intermediate in form between gymnosperms and angiosperms. Botanists still disagree upon the mechanisms of how flowering plants evolved, but one possible path is via the gnetophytes -- Ephedra - like plants evolving from conifers, then Gnetum-like plants, and angiosperms from there. But it could be the case that botanists place the plants in the same group only because they're all so damned weird.
Gnetophytes appeared during the Triassic Period. Like conifers and cycads, the plants' seeds come in small cones, but the plants exhibit some angiosperm-like properties. To the layman, the most recognizable of these would be the appearance of the leaves, indistinguishable from angiosperm leaves for the most part. Gnetophyte sex organs are uniformly weird but often resemble failed attempts to make flowers. Ephedra, in parcicular, bears brightly-colored male sporangia (pollen-cones) that most people would call a "flower" if they didn't know better. Members of Gnetum have a vine-like habit and their cones resemble berry clusters.
Gnetophyta can also be identified (except in Welwitschia) by the particular "ephedroid" character of their pollen grains - Elongated, with parallel ribs running down the length of the grain. Some gnetophyte-like conifers such as the Triassic Period's Masculostrobus exhibit ephedroid pollen. Other gnetophyte-like plants appeared in the Cretaceous, right before flowering plants appeared.
Given the division's sparse membership, its taxonomic tree is a bit degenerate. Each of the three extant genera is placed in its own family and order. I haven't found the placement of extinct gnetophyte genera such as Eoanthus and Piroconites.
Class Gnetopsida:
- Order Ephedrales - Family Ephedraceae - Ephedra (40-50 species)
- Order Gnetales
- Drewria (Cretaceous, EXTINCT)
- Family Gnetaceae - Gnetum (30-40 species)
Class Welwitschiopsida - Order Welwitschiales - Family Welwitschiaceae - Welwitschia
The strangest-looking gnetophyte is Welwitschia mirabilis, which grows only in the fog zone of the Namib Desert. It grows exactly two leaves from a central turnip-like body. As the plant grows (some Welwitscia specimiens in Namibia are close to 2000 years old), wind and sand tends to shred the leaves into long green strips, making the plant look like, well, a houseplant you forgot to water for a month, or a pile of hair in the middle of the desert.
____
\`. '--._
\ `-. `-._
\ `-. `-._
\ `. `-._
\ `. `-.
\ `. `-.
\ `. `.
\ \ \
`. \ |
`. \ /
`. | /
`-. | .'
`. | .--'
___|||__
.-*=**=*-*`.
|*=*=*====__'
__.'|`.____
.- \ `-._
/ \ `-.
| \ `.
| \ \
\ \ \
\ \ |
\ \ /
`. \ /
`-._ \ .'
`-._ \ .'
'. \.'
`./
Gnetophyta: An Enigmatic Group of Seed Plants by Thorsten Hebben, Univerity of Alberta
http://www.biology.ualberta.ca/courses.hp/bot511/index.htm
Welwitschia And Ephedra: Remarkable Genera of Gymnosperms
http://waynesword.palomar.edu/welwit.htm