Three new Critically Endangered Inversodicraea (Podostemaceae) species from Tropical Africa: I. senei, I. tanzaniensis a
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ISSN: 0075-5974 (print) ISSN: 1874-933X (electronic)
Three new Critically Endangered Inversodicraea (Podostemaceae) species from Tropical Africa: I. senei, I. tanzaniensis and I. botswana Martin Cheek1 , Olivier Séné2 & Eric Ngansop3
Summary. Three new species of Inversodicraea (Podostemaceae), I. senei from the Memv’ele falls of the Ntem River, Cameroon, I. tanzaniensis from the Ruhudji River near Lupembe, Southern Highlands, Tanzania, and I. botswana from the Kasane rapids on the Chobe River, Botswana, are described and illustrated. All three species are known from single sites. All three are assessed as Critically Endangered using the IUCN standard. With 35 species, Inversodicraea is the most species-diverse genus of Podostemaceae in continental Africa, to which it is endemic. Four species of Inversodicraea are now known to be sympatric and point endemics at Memv’ele Falls in Cameroon where a hydro-electric dam is being constructed, threatening them with global extinction. Equally, I. tanzaniensis is threatened by proposed hydro-electric projects in Tanzania. In contrast, I. botswana is threatened by sewage discharge and also by bridge construction. Key Words. Botswana, Cameroon, extinct, hydroelectric, rheophytes, Tanzania, waterfalls.
Introduction Inversodicraea Engl. has been resurrected to accommod a t e t h o s e s p e c i e s p r e v i o u s l y i n c l u d ed i n Ledermanniella subg. Phyllosma C.Cusset (Thiv et al. 2009; Schenk et al. 2015; Cheek & Haba 2016a). Inversodicraea is distinguished from Ledermanniella by the presence of scale-leaves (absent in Ledermanniella), and by having terete or laterally compressed leaf petioles (in Ledermanniella canaliculate or dorsiventrally compressed) (Cheek et al. 2017a). This paper builds on the recent synoptic account of Inversodicraea which recognised 30 species (Cheek et al. 2017a). Subsequently two more species were discovered, Inversodicraea tassing Cheek, and I. koukoutamba Cheek (Cheek et al. 2019b). Material collected in Cameroon, Tanzania and Botswana represents three additional new species which are described in this paper as I. senei Cheek, I. tanzaniensis Cheek and I. botswana Cheek respectively. This increases to 35 the number of species in Inversodicraea, the most species-diverse genus of Podostemaceae in Africa, ahead of Ledermanniella Engl. which has 30 species. Approximately 2000 new flowering plant species are described each year (Willis 2017), adding to the estimated 369,000 already known to science (Nic Lughadha et al. 2016) although this total is disputed (Nic Lughadha et al. 2017). Widespread species tend to have already been discovered, so that many newly
discovered species are range-restricted and so are much more likely to be threatened, such as those three described in this paper. Evidence-based conservation assessments exist for about 21 – 26% of known species, and 30 – 44% of these assessments rate the species concerned as threatened (Bachman et al. 2018). This makes it imperative to discover and publish such species so that they can
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