Paleobotany II: Flowering plants

from Cornell University BIOG1445
Seed review: Ancestrally, the ovule develops on the surface of a specialized leaf, such as the cone scales of living acrogymnosperms.

When we get past the paraphyletic grade group of "seed ferns," Tracheophyta contains two major groups:

Acrogymnospermae: (Devonian - Quaternary) Deemed paraphyletic in earlier literature, the traditional "gymnosperms" have emerged from recent molecular analyses as a monophyletic group. An interesting fact for its own sake, but also because it implies that the evolutionary "roots" of flowering plants go back to the mid-Paleozoic.

A fourth group requires notice:

Welwitschia mirabili from Nature Hills Nursery
Gnetophyta: (Ephedra, Welwitschia, and Gnetum.) Triassic-Quaternary. Weird arid adapted plants with flower-like strobili that enclose the ovule in an integument that is open at the end.

Until recently, we would have presented Gnetophyta as close relatives of flowering plants, however strong recent molecular evidence indicates that they are actually nested within Pinales - counterintuitive but strongly supported.

Anthophyta: Carboniferous - Quaternary) The total group of flowering plants and their kin. The familiar term Angiopspermae refers to the crown-group.

from HMH School Publishers
Before addressing the evolution of the innovations, of flowering plants, bet to have a sense of where we are headed. Simply to say that flowering plants are distinguished by flowers would be sort of dumb. In fact, flowers represent three major innovations:

Anthophyte Evolution:


(Cretaceous - Quaternary) The crown group of living anthophytes.

Angiosperms appear unambiguously in the fossil record in the Early Cretaceous. Today, they are the dominant plant type, with over 200,000 known species (compared to 550 species of gymnosperms).

Both the ecologies of their fossil relatives Sanmiguelia and Archaefructus, and of their basal living members suggest that they inhabited wetlands.

Lichnomesopsyche gloriae from Smithsonian Science

Angiosperm partners:

We've noted the big angiosperm innovation - the use of animal commensalists to pollinate flowers and disperse seeds. Who were these? Some speculation:

from Effective and creative lesson plans!

Angiosperm diversity:

Yellow stargrass - Hypoxis hirsuta

Amborella trichopoda male flower from David Tng
Basal Angiosperms:

But we note that water-lilies have endosperm that is merely diploid - a plesiomorphy or autapomorphy?