Pronephrium subg. Menisciopsis
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Taxonomy
The type species, P. lakhimpurense, is distributed from N.E. India to southern China and southwards to northern Thailand and Vietnam. It has large entire pinnae with many pairs of anastomosing veins, the excurrent veinlets all free; the sori of large plants spread all along the veins, the sporangia lacking setae. In these characters it is very close to the species of Meniscium of tropical America, and differs from them most conspicuously in the red colour of dried fronds. Another species of the same distribution in Asia, P. penangianum (Hook.) Holttum, has narrower pinnae which are strongly crenate-serrate and distal excurrent veinlets not free. In Malesia, P. rubrinerve, P. rubidum and P. scopulorum are clearly related to the two species of mainland Asia, but their sori are not more than slightly elongate; only in P. rubidum are excurrent veinlets all free.
Agreeing with the species mentioned above in the reddish colour of dried fronds and also in elongate sori are species of another Malesian group which are distinguished by having hooked hairs on frond-axes and usually also on sporangia; formerly these species were all included in Meniscium. Several of them have buds at the bases of pinnae. They are here included in section Grypothrix.
There remain three species which appear to be somewhat intermediate between the two groups above mentioned. Of these, P. acanthocarpum has buds at the bases of its pinnae as in sect. Grypothrix but sori not elongate and straight setae on its sporangia. The other two, P. nitidum and P. repandum, have similar sori and sporangia but no buds on the frond; they are very similar to each other in general aspect but differ in sporangia and spores. They are possibly a connecting link between subgenera Pronephrium and Menisciopsis. They are here placed in section Menisciopsis.
The earlier-described species of this group were much confused by Hooker, and it was not until the work of Ching in 1938 that their taxonomy and nomenclature were clarified. Ching however did not notice the hooked hairs which are the distinctive feature of sect. Grypothrix.
Agreeing with the species mentioned above in the reddish colour of dried fronds and also in elongate sori are species of another Malesian group which are distinguished by having hooked hairs on frond-axes and usually also on sporangia; formerly these species were all included in Meniscium. Several of them have buds at the bases of pinnae. They are here included in section Grypothrix.
There remain three species which appear to be somewhat intermediate between the two groups above mentioned. Of these, P. acanthocarpum has buds at the bases of its pinnae as in sect. Grypothrix but sori not elongate and straight setae on its sporangia. The other two, P. nitidum and P. repandum, have similar sori and sporangia but no buds on the frond; they are very similar to each other in general aspect but differ in sporangia and spores. They are possibly a connecting link between subgenera Pronephrium and Menisciopsis. They are here placed in section Menisciopsis.
The earlier-described species of this group were much confused by Hooker, and it was not until the work of Ching in 1938 that their taxonomy and nomenclature were clarified. Ching however did not notice the hooked hairs which are the distinctive feature of sect. Grypothrix.