Christella
Content
Distribution
Africa present, neotropics present present, warmer parts of the Old World present
About 50 spp.; throughout the warmer parts of the Old World; one species (C. hispidula) also in the neotropics; in addition c. 15-20 spp. in Africa and the neotropics the status of which still needs to be established.
Taxonomy
Leveille characterized his genus as follows: pinnae lobed, with simple veins pinnately arranged in the lobes, sori with reniform indusia, seated on the veins in a row on each side of the costules. No type species was indicated. The characters apply to most species of Thelypteridaceae, and Leveille's list included representatives of four genera as arranged in the present treatment, also two which do not belong to the family. Three of his species were transferred to other genera by Ching; several others do not strictly conform to Leveille's own generic definition. Three of his species are closely allied and belong to a group recognized by me in my preliminary studies of the family, for which I was seeking an appropriate generic name; I therefore chose a species from this group as type. In 1964 Iwatsuki had cited an allied species, C. dentata, as type of Thelypteris subg. Cyclosoriopsis, but his definition of the subgenus would include many species which seem to me not nearly allied.
In the earlier literature the species of this genus were not clearly distinguished, so that there is much confusion in the use of names. I have not attempted to assign meanings to all names cited; e.g. Aspidium patens, A. nymphale and A. parasiticum in Blume's 'Enumeratio' of 1828 are not clearly distinguished and I have not found the particular specimens to which he gave those names, which were copied from earlier works by others, who had described them very briefiy.
The single most distinctive character is the presence of an elongate unicellular gland on the stalks of sporangia (shown in Schott's figure of 1834 but mentioned by no-one eise); similar glands are also present on the lower surface of pinnae in some species. This character is associated with others less precisely definable, among them the rather thick protuberances or ridges of the perispore, a character shared by Amphineuron. But the elongate gland on the sporangium-stalk is lacking in a group of four species in New Guinea, for which I propose a new section as follows: Leptochristella Holttum, sect. nov.
In the earlier literature the species of this genus were not clearly distinguished, so that there is much confusion in the use of names. I have not attempted to assign meanings to all names cited; e.g. Aspidium patens, A. nymphale and A. parasiticum in Blume's 'Enumeratio' of 1828 are not clearly distinguished and I have not found the particular specimens to which he gave those names, which were copied from earlier works by others, who had described them very briefiy.
The single most distinctive character is the presence of an elongate unicellular gland on the stalks of sporangia (shown in Schott's figure of 1834 but mentioned by no-one eise); similar glands are also present on the lower surface of pinnae in some species. This character is associated with others less precisely definable, among them the rather thick protuberances or ridges of the perispore, a character shared by Amphineuron. But the elongate gland on the sporangium-stalk is lacking in a group of four species in New Guinea, for which I propose a new section as follows: Leptochristella Holttum, sect. nov.
Cytology
Base chromosome number 36. C. dentata, C. parasitica and C. subpubescens are tetraploid, C. hispidula diploid. Experimental hybridization of these species was undertaken at Leeds (see Holttum 1976, p. 295); C. dentata and C. parasitica were shown to be allotetraploids with C. hispidula as one parent of each. C. arida has been shown to be diploid in northern India but has not been experimentally hybridized with tetraploids. It is evident that natural hybrids between some of the commoner species have also developed, but it is difficult to assign a parentage to them.