Ferns

Pteridophytes are the division of plants that include the ferns and so-called fern allies. This is an extremely diverse group of approximately 12,000 species of plants, so divergent that in some classifications, they have been placed in four divisions (e.g., Cronquist et al. 1966). However, three common features unite the group: 1) They are not flowering plants, but instead produce and are dispersed by spores, rather than seeds; 2) They feature a complicated life cycle that includes an alternative of generations, with germination of spores into a gametophyte generation, which is haploid (containing half the normal chromosome number, n) and usually short-lived and inconspicuous and cannot themselves produce spores, but are essential to the reproductive cycle and that exists in a separate stage from the spore-producing plants, sporophytes, which are usually perennial and conspicuous, and have roots, stems (often rhizomatous), and leaves, and are diploid, with 2n chromosomes. 3) They require free (standing) water in order to reproduce, because their flagellate sperm swim to fertilize the eggs; for this reason, many of the species live in moist habitats. In addition to sexual reproduction through the alternation of generations, many pteridophytes reproduce extensively through vegetative (clonal) propagation, typically from rhizomatous stems, but also from leaves and roots. Because of this, sterile hybrid forms that arise may persist and become common in local regions. In all but a couple of genera, modern pteridophytes lack secondary growth, including cambium tissue (which produces cork cells and bark on trees). Their characteristics remain similar those found in many of the earliest land plants. However, in contrast to mosses (Bryophyta), they are vascular plants, containing vessels (xylem and phloem) to transport water and nutrients through the stem tissues. Although no single fern species is of widespread economic importance, over 700 species from 124 genera are grown as ornamentals, either indoors or outdoors for landscaping, and some species are increasingly used in North Amerian gardens where browsing by white-tailed deer (Odocoileus virginiana) is a problem. (Ferns in general are less likely to be browsed by deer than grasses and flowering species, but cultivars of fern species including Athyrium, Dryopteris, and Osmunda are particularly promoted as deer resistant.) Ferns are also sometimes used as a food plant--the emerging stems of some species are gathered in the wild and eaten as a vegetable (fiddlehead ferns, actually the unfurling leaves of various fern species, including Pteridium aquilinum (bracken fern), Matteuccia struthiopteris (ostrich fern), Osmunda cinnamomea (cinnamon fern or buckhorn fern), Osmunda regalis (royal fern), and Athyrium esculentum (vegetable fern), although some of these species are reported to contain potential carcinogens. Many fern species also have traditional medicinal uses. (Cronquist et al. 1966, Hoshizaki and Moran 2001, Moran 2004, Wagner and Smith 1993, Wikipedia 2012.)

The vascular plants (or tracheophytes) are characterized by the presence of vascular tissue (xylem and phloem) for structural support and for long-distance movement of water and nutrients throughout the plant body.

The relationships among the major groups of vascular plants have become clearer in recent years. Investigations into the origin and evolution of the major groups of vascular plants indicate that there is a deep division of the vascular plants into two lineages. One of these lineages includes only the lycophytes (clubmosses, spikemosses, and quillworts), accounting for less than 1% of vascular plant species. The other lineage (known as Euphyllophyta) includes two major clades: the spermatophytes or seed plants (including more than 250,000 species of angiosperms [flowering plants], conifers, cycads, gnetophytes, and the Gingko) and the monilophytes or ferns (sensu lato, including the horsetails, whisk ferns, and eusporangiate and leptosporangiate ferns, with most of the roughly 12,000 monilophyte species being leptosporangiate ferns).

(Pryer et al. 2001; Pryer et al. 2004; Smith et al. 2006; Lehtonen 2011 and references therein)

The horsetails or scouring rushes (Equisetophyta, Sphenophyta, Arthrophyta, and Equisetaceae are among the names that have been used for this group) are now believed to form a monophyletic group with the ferns that is known as the "monilophytes" (although the position of the horsetails within the monilophytes is not yet fully resolved, they may be nested among other ferns);this clade, in turn, is the sister group to the seed plants (Pryer et al. 2001; Schneider et al. 2009 and references therein; Rai and Graham 2010 and references therein). There is just one extant genus, Equisetum, which includes around 15 extant species. Equisetum is nearly cosmopolitan (not native to Australia and New Zealand, but they are exotic weeds there). Many Equisetum have a high silica content and can be used to scour pots (explaining the name "scouring rush"). Horsetails have an extensive and diverse fossil record and several hundred million years ago widespread tree-sized relatives reached 30 m in height (even today, some Equisetum species can reach an impressive size--although nothing approaching 30 m!).

(Mabberley 2008)

For more information on the biology of horsetails, see Husby (2013) and Chad Husby's website.

The relationship of "pteridophytes" to other vascular plants (= tracheophytes) has become clearer in recent years. Investigations into the origin and evolution of the major groups of vascular plants indicate that there is a deep division of the vascular plants into two lineages. One of these lineages includes only the lycophytes (clubmosses, spikemosses, and quillworts). The other lineage includes two major clades: the spermatophytes or seed plants (including more than 250,000 species of angiosperms [flowering plants], conifers, cycads, gnetophytes, and the Gingko) and the monilophytes or ferns (sensu lato, including the horsetails, whisk ferns, and eusporangiate and leptosporangiate ferns, with most of the roughly 12,000 monilophyte species being leptosporangiate ferns). The spermatophytes and monilophytes together comprise a clade known as Euphyllophyta.

Plants in the lycophyte and monilophyte clades are apparently not each other's closest relatives (since the monilophytes are believed to be sister to the seed plants), but because they both produce spores and not seeds, the lycophytes and ferns have traditionally been grouped together in what is now generally recognized to be a paraphyletic group referred to as "pteridophytes" or "ferns and fern allies".

(Pryer et al. 2001; Pryer et al. 2004; Smith et al. 2006; Lehtonen 2011 and references therein)

Ferns of Arizona - Arizona, USA
Ontario Ferns - Ontario, Canada
Identifying Australian Rainforest Plants,Trees and Fungi: Ferns - Australia