Afrothismiaceae (Dioscoreales), a new fully mycoheterotrophic family endemic to tropical Africa

Abstract

SummaryAfrothismia is a genus of non-photosynthetic mycoheterotrophs from the forests of continental tropical Africa. Multiple phylogenetic inferences using molecular data recover the genus as sister to a clade comprising mycoheterotrophic Thismiaceae and the photosynthetic family Taccaceae, contrary to earlier placements of Afrothismia and Thismiaceae within Burmanniaceae. Morphological support for separating Afrothismia from the rest of Thismiaceae has depended on the zygomorphic flowers of Afrothismia (although some species of Thismia are also zygomorphic), and their clusters of root tubers, each with a terminal rootlet. The number of described species of Afrothismia has recently increased from four to 16, with seven more species as yet undescribed; these discoveries have added morphological characters that support its distinction from Thismiaceae. Most notably, the ovary in Afrothismia has a single stalked placenta, and circumscissile fruits from which seeds are exserted by placental elevation (vs in Thismiaceae, three placentas, a deliquescing fruit lid, and seeds not exserted). Afrothismia stamens are inserted in the lower part of the floral tube, where they are attached to the stigma, and individual flowers are subtended by a single large dorsal bract. In contrast, in Thismiaceae, stamens are inserted at the mouth of the tube, free of and distant from the stigma, and each flower is subtended by a loose whorl of (2 –) 3 (– 4) bracts. Here we formally characterise Afrothismiaceae and review what is known of its development, seed germination, interactions with mycorrhizal Glomeromycota, biogeography, phylogeny and pollination biology. All but one (Afrothismia insignis; Vulnerable) of the 13 species assessed on the IUCN Red List of Threatened Species are either Endangered or Critically Endangered; one species (A. pachyantha) is considered extinct.

Keetia nodulosasp. nov. (Rubiaceae - Vanguerieae) of West - Central Africa: bacterial leaf nodulation discovered in a fourth genus and tribe of Rubiaceae

“…(Afrothismiaceae, Cheek & Williams 1999; Cheek et al . 2019; Cheek et al . 2023d) and at least two species of the African genus Inversodicraea (Cheek et al .…”

“…(Thismiaceae,Cheek et al 2018b) and Afrothisia pachyantha Schltr. (Afrothismiaceae,Cheek & Williams 1999;Cheek et al 2023d) and at least two species of the African genus Inversodicraea(Cheek et al 2017), are well known examples, recently joined by species such as Vepris bali Cheek (Rutaceae,Cheek et al 2018c), Vepris montisbambutensis Onana(Onana & Chevillotte 2015) and Ardisia schlechteri Gilg (Murphy…”

Keetia korupensis sp. nov. (Rubiaceae - Vanguerieae) a threatened lowland evergreen forest climber and the endemic plant species of Korup National Park, SW Region, Cameroon

“…(Afrothismiaceae, Cheek & Williams 1999; Cheek et al . 2019; Cheek et al . 2024) are well known examples, recently joined by species such as Vepris bali Cheek (Rutaceae, Cheek et al .…”

Ubiquitous arbuscular mycorrhizal fungi in the roots of herbaceous understory plants with hyphal degeneration in Colchicaceae and Gentianaceae

“…Among mycoheterotrophic plants, Orchidaceae and Ericaceae plants have been found to associate with Basidiomycota and Ascomycota, whereas other plant families associate with Glomeromycotina (i.e., AM fungi). There are at least 330 species of mycoheterotrophic AM plants in nine angiosperm families (Merckx et al 2013b ; Cheek et al 2024 ; Imhof 2024 ), and Paris -type AM have been observed in all plants examined (Imhof et al 2013 ). Recently, Giesemann et al ( 2021 ) suggested that partial mycoheterotrophy (mixotrophy), obtaining carbon compounds via both photosynthesis and mycoheterotrophy, may be common among chlorophyllous plants with Paris -type AM based on the enrichment of 13 C and 15 N. Along with the observation that understory plants typically develop Paris -type AM (Brundrett and Kendrick 1990 ; Yamato and Iwasaki 2002 ), it has been suggested that Paris -type AM may be a prerequisite for the evolution of mycoheterotrophy (Imhof 1999 ; Giesemann et al 2021 ).…”