Height of Seedless Vascular Plants

Pterophyta

• The Pterophyta or fern family, which dates back 300 million years, contains 240 genera and more than 10,500 species. Among these are some of the tallest seedless vascular plants, known as tree ferns (Dicksonia spp.). The New Zealand tree fern (D. squarrosa) is grown as an ornamental. This fern grows from 25 to 30 feet tall and has large, feathery, evergreen fronds. These huge ferns grow slowly and thrive in shaded, moist sites. At the other end of the size spectrum, the smallest fern grows from 1 to 5 inches tall. The wall-rue (Asplenium ruta-muraria) grows naturally in rocky areas, especially those with limestone or calcareous shale. The wall-rue has toothed leaflets and a green stem.

Psilophyta

• The Psilophyta family is even older than the ferns, dating back more than 400 million years to the Devonia era. Today, only two genera still remain of this family known as whisk ferns. Psilotum grows in tropical regions of North America, Asia, the Caribbean and some Pacific Islands, and Tmesipteris grows in parts of Australia, New Zealand and New Caledonia. Whisk ferns grow to 2 feet tall with a 3-foot spread. While some whisk ferns are cultivated, most grow wild as weeds. Their Latin name stems from the word "nude," and indeed these ancient plants do not have roots, leaves, fruits, seeds or flowers. Rather, whisk ferns form as a series of stems that grow both above and beneath the soil. They gather water through a series of underground stems known as rhizomes that exist in a symbiotic relationship with a fungi that helps them absorb moisture. Like ferns, they reproduce through spores.

Lycophyta

• The Lycophyta family contains only two genera, the Lycopodium and Selaginella. Lycopodium grows naturally in damp forest understories across the globe. Lycopodiums also have rhizomes, but unlike the whisk ferns, they have small leaves known as microphylls. Some species are cultivated as ground covers and are often used as filler in floral arrangements. Selaginella shares a similar structure with Lycopodium, but it grows in the tropics. Selaginella have differently sized spores, while Lycopodiums are homosporous.

Sphenophyta

• The Sphenophyta family contains only the Equisetum or horsetail genus. Also known as scouring rushes, these jointed, air-filled plants grow throughout the globe and tend to colonize in damp to wet sites. Most have very small whorled leaves and some produce light, feathery-looking branches. Horsetails are homosporous and are generally considered weeds, though a few species are grown as ornamentals in aquatic gardens. Though in the Paleozoic era some species grew up to 100 feet tall, most modern horsetails grow between 1 and 10 feet.