Blechnum

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Blechnum

Description

Terrestrial and lithophytic ferns. In Malesia none is persistently epiphytic.

Distribution

southern hemisphere: present
The majority of species are in the Southern Hemisphere.

Morphology

Reference to the frond includes the stipe, rhachis, and the lamina. The rhachis is limited to the zone of the lamina that produces leafy outgrowths. The stipe does not give rise to leafy outgrowths but may in some species give rise to non leafy structures. In some species the stipe is very short in relation to the lamina. In many of the lomarioid species the stipe of the fertile frond is very much longer than the stipe of the sterile frond; this is especially so in species that produce fertile fronds seasonally. The lamina of most species of the genus is pinnate, pinnatifid, or pinnatisect. An entire lamina when occurring is in most cases produced at an early stage in the development of a plant. Bipinnate, bipinnatifid, and bipinnatisect subdivisions are rare and only occur in one species in the Malesian region, but these conditions are also occasionally found in mutant individuals of some other species. The rhizome is a variable structure and when woody and growing erect is referred to as a caudex. A few species produce a caudex sufficiently tall for the plants to be regarded as small tree-ferns. Some species produce a slender creeping rhizome which may be either above ground or subterranean and these can give rise to colonies from one individual; other species produce a massive subterranean rootstock. All species of the genus Blechnum in the Malesian region are primarily terrestrial; occasionally in very humid habitats some species may be epiphytic, usually on fallen logs and rarely if ever high off the ground; none are true lianas.

The characters used to describe the perine and exine features of the spores are as defined in the glossary of Large & Braggins (1991: 160-163). The number of herbarium specimens from which spore preparations were examined is indicated, along with the average measurement of spores. — , .

Cytology

The probable base numbers are 28 and 33 but with a considerable range reported from 28 to 40. Polyploidy (tetraploidy and triploidy) has been reported in some taxa.

Notes

1. The size of mature spore-bearing plants is variable not only from species to species but, in the more plastic species, from plant to plant; this is often a response to ecological conditions.
2. While all species have distinctive, small, early post-prothallial fronds, a few also have very distinctive juvenile foliage, including B. melanocaulon subsp. melanocaulon, B. melanocaulon subsp. pallens, B. patersonii subsp. queenslandicum, and B. finlaysonianum. Blechnum finlaysonianum is particularly striking as the entire and the lobed fronds of the juvenile state are very different from the exceptionally large pinnate fronds characteristic of mature plants. Only one species (B. fraseri) in Malesia is bi-pinnatifid.
3. Many (but not all) of the species are readily recognised by their frond pattern. The identification of several species requires careful examination of basal stipe, rhachis, and costal scales.
4. One taxon, B. vulcanicum, and its variants, requires examination for the presence of characteristic pale brown or buff, linear, uniseriate multicellular hairs. While these are usually abundant there are variants in which a detailed search has to be made for these hairs. Several other species which are not closely related to B. vulcanicum have hairs, but they are of quite different character.
5. Spore characters are useful for some species. We have used herbarium material examined by scanning electron microscopy (, ). In some taxa there is variation, more in degree than type, of ornamentation. In one instance the strikingly different spore type of offshore island populations has resulted in the detection and description of a previously undescribed species. At this stage this new species (B. nesophilum) has only been found in collections from islands north and east of Papua New Guinea.