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The gymnosperms (/ ˈ dʒ ɪ m n ə ˌ s p ɜːr m z,-n oʊ-/ ⓘ nə-spurmz, -noh-; lit. ' revealed seeds ') are a group of woody, perennial seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include conifers, cycads, Ginkgo, and gnetophytes, forming the clade Gymnospermae [2] The term gymnosperm comes from the ...
The oldest fossil evidence of seed plants is of Late Devonian age, and they appear to have evolved out of an earlier group known as the progymnosperms. These early seed plants ranged from trees to small, rambling shrubs; like most early progymnosperms, they were woody plants with fern-like foliage.
The apricot-like structures produced by female ginkgo trees are technically not fruits, but are seeds that have a shell consisting of a soft and fleshy section (the sarcotesta), and a hard section (the sclerotesta). The sarcotesta has a strong smell that most people find unpleasant.
The tree-like Archaeopteris, ancestral to the gymnosperms, and the giant cladoxylopsid trees had true wood. These are the oldest known trees of the world's first forests. Prototaxites was the fruiting body of an enormous fungus that stood more than 8 meters tall. By the end of the Devonian, the first seed-forming plants had appeared.
[10] [6] Differing sized spores have been observed in many fossilized plant species. [7] For example, the species Lepidophloios, also known as the scale tree, has been shown in fossils to have been heterosporous; [6] The scale tree had separate cones containing either male or female spores on the same plant. [6]
The extinct arboreal plants of the genera Lepidodendron and Sigillaria were the first to have distinct aeration structures that rendered these modifications. "Parichnoi" (singular: parichnos) are canal-like structures that, in association with foliar traces of the stem , connected the stem's outer and middle cortex to the mesophyll of the leaf .
This cycle is known as alternation of generations. The spores of seed plants are produced internally, and the megaspores (formed within the ovules) and the microspores are involved in the formation of more complex structures that form the dispersal units, the seeds and pollen grains.
Trees are not a monophyletic taxonomic group but consist of a wide variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. The majority of tree species are angiosperms or hardwoods; of the rest, many are gymnosperms or softwoods. Trees tend to be long-lived ...