Taxonomic revision of the threatened African genusPseudohydrosmeEngl. (Araceae), withP. ebo, a new, Critically Endangered species from Ebo, Cameroon

Abstract

This is the first revision in nearly 130 years of the African genus Pseudohydrosme, formerly considered endemic to Gabon. Sister to Anchomanes, Pseudohydrosme is distinct from Anchomanes because of its 2–3-locular ovary (not unilocular), peduncle concealed by cataphylls at anthesis and far shorter than the spathe (not exposed, far exceeding the spathe), stipitate fruits and viviparous (vegetatively apomictic) roots (not sessile, roots non-viviparous). Three species, one new to science, are recognised, in two sections. Although doubt has previously been cast on the value of recognising Pseudohydrosme buettneri, of Gabon, it is here accepted and maintained as a distinct species in the monotypic section, Zyganthera. However, it is considered to be probably globally extinct. Pseudohydrosme gabunensis, type species of the genus, also Gabonese, is maintained in Sect. Pseudohydrosme together with Pseudohydrosme ebo sp.nov. of the Ebo Forest, Littoral, Cameroon, the first addition to the genus since the nineteenth century, and which extends the range of the genus 450 km north from Gabon, into the Cross-Sanaga biogeographic area. The discovery of Pseudohydrosme ebo resulted from a series of surveys for conservation management in Cameroon, and triggered this paper. All three species of Pseudohydrosme are morphologically characterised, their habitat and biogeography discussed, and their extinction risks are respectively assessed as Critically Endangered (Possibly Extinct), Endangered and Critically Endangered using the IUCN standard. Clearance of forest habitat for logging, followed by agriculture or urbanisation are major threats. One of the species may occur in a formally protected areas and is also cultivated widely but infrequently in Europe and the USA for its spectacular inflorescences.

Pseudohydrosme bognerisp. nov. (Araceae), a spectacular Critically Endangered (Possibly Extinct) species from Gabon, long confused withAnchomanes nigritianus

“…Anchomanes are 1-locular, and Pseudohydrosme 2(– 3)-locular. However, in a recent taxonomic revision of Pseudohydrosme , five additional characters separating the genera are given (Cheek et al 2021, Table 2, see discussion below). In one of these, peduncle length, the new species described here fits Anchomanes , not Pseudohydrosme .…”

“…In contrast in all four species of Pseudohydrosme , the ovary is globose or globose-ovoid, and not polygonal. The style is always symmetrical, distinct, stout, cylindric and bears a thickened, 2 – 3-lobed stigma, and the stigmatic lobes are reflexed (Mayo et al 1997: Plate 70R, Plate 71H&I, Cheek et al 2021 Fig.6G, Fig. 7E).…”

“…The new species described below as Pseudohydrosme bogneri was mainly described from herbarium specimens (gross morphological structures) and spirit preserved material (details of the spadix). The terms and format of the description follow the conventions of Mayo et al (1997) and Cheek et al (2021). Georeferences for specimens lacking latitude and longitude were obtained using Google Earth (https://www.google.com/intl/en_uk/earth/versions/).…”

“…2013; Gosline & Malecot 2011). These authors detail 19 species globally restricted to the Libreville area, of which eight have not been seen recently and which are possibly extinct (listed in Cheek et al 2021). Among these is Octoknema klaineana Pierre, a rainforest tree “only collected in the immediate area of Libreville at the beginning of the 20 th century, and only once since.” Threats in the Libreville area have already resulted in the possible global extinction of these eight species, which rise to nine with the addition of Pseudohydrosme buettneri (Cheek et al 2021) and ten when P. bogneri is included.…”

“…Moreover, re-examination of Bogner’s material shows it to have the key features of Pseudohydrosme , a genus of three species closely related to Anchomanes but centred in Gabon, and which was recently revised (Cheek et al 2021). In this paper we describe morphologically the taxon represented by Bogner’s material for the first time, and we test the hypothesis that it is a fourth, hitherto undescribed species of Pseudohydrosme .…”