Gymnosperm

Evolution of Seeds (3 of 3)
• As megasporangia evolved into ovules with integuments, other telomes on nearby branches became modified into cupules (similar to carpels in flowering plants).
• Simultaneously, microspores were evolving into pollen grains.

Division Pteridospermophyta:
Seed Ferns (1 of 2)
• Progymnosperms gave rise to another line of gymnospermous plants in addition to the conifers, the cycadophytes.
• These are classified as three divisions.
− Pteridospermophyta (seed ferns, all extinct)
− Cycadophyta (cycads, extant)
− Cycadeoidophyta (cycadeoids, all extinct)
• Not all seed ferns are closely related to each other; they form a grade instead of a clade.

Division Pteridospermophyta:
Seed Ferns (2 of 2)
• Pteridosperms are thought to have evolved from the Aneurophytales because the earliest seed ferns had a three-ribbed protostele.
• Seed ferns were any woody plant with fernlike foliage that bore seeds instead of sori.
• Leaves of seed ferns were similar to those of true ferns in overall organization—large, compound, and planar.

Division Coniferophyta: Conifers (1 of 8)
• Conifers are the most diverse group (approximately 50 genera and 550 species), and all are trees of moderate to gigantic size.
• Conifer leaves are always simple needles or scales, and most are perennial.

Division Coniferophyta: Conifers (2 of 8)
• The venation of conifer leaves is often simple, with just one or two long veins running down the center of a needle-shaped leaf or several parallel veins in scale-shaped leaves.

Division Coniferophyta: Conifers (3 of 8)
• Just as in their progymnosperm ancestor Archaeopteris, wood of modern conifers lacks vessels, and their phloem lacks sieve tubes.
• All conifers have pollen cones and seed cones, most of which are woody.
• Pines, like several other conifers, have two types of shoot.
− Tiny papery leaves occur on long shoots and in their axils are short shoots that produce the familiar long needle leaves.

Division Coniferophyta: Conifers (4 of 8)
• Pollen cones are simple, with a single short unbranched axis that bears microsporophylls.

Division Coniferophyta: Conifers (5 of 8)
• Seed cones are more complex; they are compound cones, each consisting of a shoot with axillary buds.