Gymnosperm means 'naked seed', and they are Earth's most threatened plants
Pines, cycads, the ginkgo and the bizarre Welwitschia share one feature: their seeds sit exposed on scales or leaves instead of tucked inside a fruit. That lineage split from the ancestors of flowering plants over 300 million years ago, and today gymnosperms are the most endangered group of plants on the planet.
The name joins Greek words for naked and seed. Flowering plants, the angiosperms, enclose their ovules in an ovary; gymnosperms carry theirs openly, usually on cone scales, though yews, Torreya and Ginkgo bear seeds singly. All are woody perennials, and not one herbaceous species exists. More than 1,000 living species remain, grouped into 12 main families and 83 genera. Conifers dominate, with around 600 to 630 species; cycads, small palm-like trees mostly found near the equator, number about 338; gnetophytes add 95 to 100; and the ginkgo stands alone.
Their origins were long placed in the Late Carboniferous, when they replaced tropical lycopsid rainforests, but newer phylogenetic work suggests they split from angiosperm ancestors in the Early Carboniferous. A whole-genome duplication around 319 million years ago seems to have fuelled their later spread, and seed-like features already show in progymnosperm fossils about 383 million years old. Long before bees met flowers, some extinct gymnosperms of the mid-Mesozoic were apparently pollinated by scorpionflies with long mouthparts that sipped pollination drops, and others by kalligrammatid lacewings.
Reproduction happens in two main ways. Pollen, carried by wind or insects, slips through a tiny opening in the ovule called the micropyle. In cycads and ginkgo it then releases sperm that swim to the egg; in conifers and gnetophytes the sperm lack tails and travel down a pollen tube. Several embryos usually start in each seed. About 65 percent of gymnosperms have separate male and female plants, but conifers nearly all carry both sexes on one tree and rely entirely on wind. Cycads host nitrogen-fixing cyanobacteria in special coral-shaped roots, while pines partner with fungi.
Despite their limited range of niches, the group includes oddities: a parasitic conifer, an epiphytic cycad and a species adapted to fast-flowing rivers. The first gymnosperm genome, Norway spruce, was published in 2013. Pine, fir, spruce and cedar supply lumber, paper and resin, and gymnosperm products turn up in soap, varnish, nail polish, gum and perfume.
Source: Gymnosperm
