Lygodium

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Lygodium

Distribution

Japan: present New Zealand: present Pantropic: present S. Africa: present eastern U.S.A. to Massachusetts: present
Pantropic, comprising c. 40 spp., also extratropical southwards in New Zealand and S. Africa, northwards in Japan and in eastern U.S.A. to Massachusetts.

Morphology

Owing to the peculiar structure of the climbing leaves, it is difficult to apply the usual descrip- tive terms pinna and pinnule to them, especially where the branching of the leafy parts is dichotomous. The following terms are here used. The climbing rachis of the frond (sympodial in structure but for convenience considered as a unit) bears alternate short primary branches, each ending in a dormant apex and bearing a pair of apparently opposite secondary branches. The secondary branches may bear leaflets or tertiary branches pinnately arranged, or they may be once or more times dichotomously branched.
The narrow wings on rachis-branches of all orders, those of the ultimate branches joined to the edge of the lamina, correspond with the wings which are the only lamina in fronds of Schizaea, but do not have the very regular single rows of stomata found in Schizaea (there are irregularly scattered stomata on both sides of a wing in Lygodium). If the sorophores of Lygodium are regarded as homologous with the fertile leaflet-lobes of the paleozoic fossil genus Senftenbergia, the lamina of Lygodium may be considered as a specialized development of the rachis-wing consequent on the reduetion of the original lamina-lobes to sorophores.
The dormant apices of the primary rachis-branches are covered with septate hairs. In a group of Malaysian species these hairs have swollen bases, each base formed of a mass of cells; these species are L. borneense, L. longifolium, L. auriculatum, L. trifurcatum, and L. dimorphum. So far as I know, this type of hair has not hitherto been reported in Lygodium.

Taxonomy

There are four pairs of species which in some measure intergrade. These need experimental study in cultivation to discover how much variation is due to environmental conditions, and also cyto- logical study. It may be that natural hybridization occurs, and as tetraploids as well as diploids have been already discovered in L. japonicum and L. circinnatum they may occur also in other species, leading to the possibility of the formation of sterile triploids; apogamy has however not yet been discovered in the genus. The pairs of species which intergrade are: L. flexuosum and L. japonicum; L. ßexuosum and L. salicifolium; L. borneense and L. auriculatum; L. dimorphum and L. trifurcatum. The following species are very distinct: L. polystaehyum, L. microphyllum, L. circinnatum, L. merrillii, and L. versteegii. L. longifolium from Singapore: n = 58, tetraploid; L. salicifolium from Perak: n = 28?, diploid. (Information from I. MANTON, in litt.).

Citation

Prantl - in Unters. Morph. Gefässkr. 1881: 60
Pichi-Sermolli - in Webbia. 1956: preprint (1955).
Copeland, Gen. Fil. 1947: 23