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

Cheek, Martin; Soto Gomez, Marybel; Graham, Sean W.; Rudall, Paula J.

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

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Journal article

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Cheek, Martin

Soto Gomez, Marybel

Graham, Sean W.

Rudall, Paula J.

Date published

November 30, 2023

Abstract

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 and Thismiaceae within Burmanniaceae. Morphological support for separating from the rest of Thismiaceae has depended on the zygomorphic flowers of (although some species of are also zygomorphic), and their clusters of root tubers, each with a terminal rootlet. The number of described species of 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 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). 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 ( ; Vulnerable) of the 13 species assessed on the IUCN Red List of Threatened Species are either Endangered or Critically Endangered; one species ( ) is considered extinct.