Uses. In Tanzania used for building poles (fide Greenway, Semsei). Conservation Widespread; least concern (LC). C. deckenii has been separated from C. manniana by many authors. The very reduced pinnae near the stipe base and the obviously one-sided (hemitelioid) indusia, were used to distinguish it from that species. Holttum (1981) recognised 4 groups and made an important distinction between species with hemitelioid sori and sori with a complete cup or disc. The type collection of C. deckenii Kuhn consists of three detached parts: one complete small pinna and two incomplete pinnae, both without sori.Pichi Sermolli (1956) in comparing deckenii with manniana, cited only the type and Alluaud 349 as representing deckenii. Both are from Kilimanjaro. He considered deckenii a distinct and probably highly localized species, and that it “was misunderstood by authors and nearly all the specimens from Tropical East Africa referred to this species are wrongly identified”, and were in fact manniana. The character states he used seem weak to me, as such can be seen to vary within a single frond of the better collections of manniana from E Africa (mostly made since 1956), and indeed the rest of Africa in which it occurs. I consider the poor type material could very well have come from near the apex of a frond, where costule distance and other parameters he uses are smaller.Holttum (1981) also upheld deckenii as a good species, without reference to the Pichi Sermolli paper. He cited five additional collections which he considered deckenii, from three widely separated locations in Tanzania, Congo Republic and Mozambique. I have examined five of these, including Allaud 349, and find that despite Holttum’s emphasis on the presence of a hemitelioid (one-sided) indusium in deckenii (which of course could not be ascertained from the rudimentary and sterile type collection), all of these collections have entire indusial cups, albeit most of them variously split in one or two places and therefore can appear to be one-sided. In addition, the folder at K containing Allaud 349 (2 sheets) has an annotation on it, in Holttum’s hand, as follows “these specimens are not closely distinct from manniana ”. This doubt is not hinted at in his 1981 paper. On checking this material through the Beck microscope and illuminator Holttum was using at Kew to examine African Cyathea in 1980–81, the images possible are indeed conclusive on this point. In addition, in his description of deckenii (enlarged to take in the seven collections he cites) he mentions the presence of reduced basal pinnae, presumably alluding to Faden 70/314, which is the only specimen of the six he saw to have a stipe base. Incidentally what appeared to him to be the base of a reduce pinna on the K set of this number is in fact an aborted pinna. Those two character states were used by Holttum (see p. 464 of his 1981 paper) to position deckenii in his ‘group 2’, along with C. capensis, which demonstrably has a one-sided indusium. Hence the position of these two names together in his key. C. manniana he placed in his ‘group 3’, with dregei and thomsonii, all of which he stated as not having reduced pinnae. My study of African collections in BM, EA, K, WAG, in particular six very good collections from East Africa (some of which were collected after 1981 or were otherwise apparently not seen by Holttum) show clearly that manniana can bear one or more (usually two) very reduced pinnae, or aborted such, near the stipe base. The aborted pinnae may be very small and inconspicuous. Hepper & Field 5186 from the West Usambaras is particularly revealing, with its long stipe and a single reduced pinna 5 cm long by 1.5 cm wide, plus a tiny aborted pinna. It also shows sori with complete indusial cups directly abutting onto sori with cups tilted and/or split in such a way as to appear hemitelioid.Interestingly, Schelpe (1970) placed deckenii in synonymy under manniana, without comment.In Zimbabwe Asplenium hypomelas seems restricted to the stems of C. manniana .