The Web of Life (49) Plants


Photosynthesis underwrites most life on Earth. ~ American botanist Karl Niklas

The grouping of plants conventionally includes the progenitor – green algae – and its land plant descendants – embryophytes. On land are mosses, liverworts, ferns, and other seedless plants (pteridophytes), gymnosperms, and angiosperms.

Mosses are small, soft, non-vascular plants. There are 12,000 different mosses: typically, 1–10 cm tall, though a few are larger.

Dawsonia is the largest moss. Found in Oceania, it can reach 65 cm in length.

Liverworts are an evolutionary step from mosses, as their leaves are more developed, and they have rhizoids: root hairs, which are the precursor to roots. There are 9,000 distinct liverworts.

Ferns were the first vascular plant. They have roots, stems, and leaves, but reproduce via spores, not seeds. Ferns first appeared 360 MYA, but the ferns living today date to 145 MYA. There are 12,000 extant species of ferns.

Gymnosperms were the first seed-producing plants (spermatophytes). Conifers, cycads, gnetophytes, and the ginkgo tree are gymnosperms.

Conifers bear their seeds in cones. There are 8 conifer families, 68 genera, and 630 extant species. Conifers include pines, cypresses, and other cone-bearers. A few conifers are shrubs, but most are trees.

Cycads have a stout, woody trunk, topped with a crown of large, stiff, evergreen leaves, which are typically pinnate. Cycads include bread palms, Zamia, and Ceratozamia.

Gnetophytes differ from other gymnosperms in having the water-conducting tissue found in all flowering plants. There are 3 genera of gnetophyte: Gnetum, Welwitschia, and Epherdra, totaling 70 species.

The Gnetum genus comprises ~35 species. Most Gnetum are woody climbers in tropical forests. The best-known Gnetum is the melinjo tree; endemic to Southeast Asia and western Pacific Ocean islands. Melinjo seeds, fruit, flowers, and leaves are used in Indonesian cuisine.

Welwitschia has a single species: an odd, large, but low-to-the-ground plant, native to the Nimib desert on the west coast of Africa. Welwitschia may live 2,000 years or more.

The Welwitschia plant has 2 strap-like leaves that grow continuously from the plant’s base, reaching 2–4 meters. Over time the 2 leaves become flayed by various events, giving the appearance of multiple straps.

Welwitschia have separate female and male plants (dioecious). Insects fertilize. Females produce seed-bearing cones.

The 50 species of Epherdra are shrubs adapted to aridity; found in southwest North America, the west coast of South America, north Africa, and temperate latitudes from Spain to China.

Epherdra have been medicinally employed for at least 60,000 years; treating asthma, hay fever, and the common cold. They contain the alkaloids ephedrine and pseudoephedrine. These compounds – chemically related to amphetamines – have both stimulant and decongestant properties.

Angiosperms enfold the latest innovations in plant technology, most notably beautiful blossoms; a sexual display of unmatched loveliness. There are 352,000 species of flowering plants.

All told, there are nearly 400,000 plant species. Over 90% are seed plants.

A plant and its environment are inextricably linked into one holistic structure. Plants are not passive entities at the mercy of any environmental perturbation, but to an extent manipulating the environment to their benefit. ~ Anthony Trewavas

Plants provide much of Earth’s breathable oxygen. Plants are the macroscopic foundation of terrestrial ecology. All land animals ultimately depend upon plants for survival.

Most plants have 3 major organs: roots, stems, and leaves. Angiosperms add flowers.