Instant Notes: Plant Biology

by bracts making the whole structure look remarkably like a flower (Fig. 1). It is

likely that some, at least, were insect-pollinated, but this structure probably

arose independently from the flowers of the angiosperms.

Another fossil group, the Caytoniales, may be ancestral to the flowering

plants, since the ovules, and later the seeds, were surrounded by cup-like

outgrowths, known as cupules (Fig. 2), resembling the ovary of flowering

plants.

One of the most abundant fossil seed plant groups in the Carboniferous period

was the Cordaitales. They were massive trees to 30 m high with simple strap-

shaped leaves, often quite large but with simple traces in the vascular system.

Their vegetative parts strongly resembled those of some living conifers such as

the monkey-puzzle, Araucaria, and they may be ancestral to conifers. Male and

female reproductive structures were separated onto different shoots, perhaps on

the same tree. Shoots of both sexes had overlapping bracts (modified leaves)

Other fossil seed
plants

294 Section R – Seed plants

5 mm

Stamens

Ovules

Sterile

scales

Fig. 1. The hermaphrodite flower-like reproductive structure of fossil Bennettitales.

Cupule

Cupule

1 cm 1 mm

Ovules

Pore

(a)

(b)

Fig. 2. The female reproductive structure of fossil Caytoniales showing cupule surrounding

the ovule.