Category: 02. Conifers (Gymnosperms)

It is generally conceded that from the pteridosperms arose members of the division Cycadophyta. The first cycads appeared in the Permian Period (298.9 million to 252.2 million years ago), although fragmentary fossils of older age suggest that cycads were present during the preceding Carboniferous Period. Some of these presumed cycads differ from extant members in that megasporophylls were undivided, unlike those…

The earliest recognized group of gymnospermous seed plants are members of the extinct division Pteridospermophyta, known as pteridosperms or seed ferns. These plants originated in the Devonian Period and were widespread by the Carboniferous. In habit, seed ferns resembled some progymnosperms in that they were small trees with fernlike leaves (the equivalent of a progymnospermous flattened branch) bearing seeds.…

Gymnosperms were the first seed plants to have evolved. The earliest seedlike bodies are found in rocks of the Upper Devonian Series (about 382.7 million to 358.9 million years ago). During the course of the evolution of the seed habit, a number of morphological modifications were necessary. First, all seed plants are heterosporous, meaning that two kinds…

The division Gnetophyta has three families across three orders: Ephedraceae, Gnetaceae, and Welwitschiaceae. The family Ephedraceae consists of about 65 species of shrubs in a single genus, Ephedra. Gnetaceae has some 30 species in the genus Gnetum, many of which are trees or vines. Welwitschiaceae consists of a single species, Welwitschia mirabilis, characterized by a massive squat stem and two leaves. Some Ephedra species may have both microstrobili…

The division Ginkgophyta consists of a single living species, Ginkgo biloba. A hardy deciduous tree, Ginkgo resembles an angiosperm in that the woody stem is frequently and irregularly branched and bears broad leaves, which are fan-shaped with dichotomously branched veins. Although it is now cultivated extensively around the world, Ginkgo is an endangered species, as its natural populations have been reduced to a small portion of the mountains…

Cycads resemble palm trees with fleshy stems and leathery featherlike leaves. The 10–11 genera and 305 living species are distributed throughout the world but are concentrated in equatorial regions. Cycads are typically short and squat, although the Australian cycad Macrozamia hopei may reach 19 metres (62 feet) in height. Given their attractive foliage and sometimes colourful cones, the…

Known as conifers, members of the division Pinophyta are among the most diverse of the gymnosperms, with some 630 living species across six families. Some of the oldest living things on Earth are conifers, including several bristlecone pines (Pinus longaeva) found in the White Mountains of California that approach 5,000 years in age. Additionally, conifers are also the tallest and most-massive living…

Scottish botanist Robert Brown first distinguished gymnosperms from angiosperms in 1825. While older classifications considered all seed plants to be assignable to a single division, Spermatophyta, more-recent classifications recognize that the characteristic of naked seeds is not important enough to be used to tie all plants with that feature into one group. Classification of gymnosperms now recognizes four extant divisions.

In all living gymnosperm groups, the visible part of the plant body (i.e., the growing stem and branches) represents the sporophyte, or asexual, generation, rather than the gametophyte, or sexual, generation. Typically, a sporophyte has a stem with roots and leaves and bears the reproductive structures. As vascular plants, gymnosperms contain two conducting tissues, the xylem and phloem. The xylem conducts water and minerals from the roots…

Gymnosperm, any vascular plant that reproduces by means of an exposed seed, or ovule—unlike angiosperms, or flowering plants, whose seeds are enclosed by mature ovaries, or fruits. The seeds of many gymnosperms (literally, “naked seeds”) are borne in cones and are not visible until maturity. Taxonomists recognize four distinct divisions of extant (nonextinct) gymnospermous plants—Pinophyta, Cycadophyta, Ginkgophyta, and Gnetophyta—with 88 genera and more than 1,000 species distributed…