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A new species of functionally dioecious bush tomato of Solanum subgenus Leptostemonum is described. Solanum scalarium Martine & T.M.Williams, sp. nov., is a member of the taxonomically challenging “Kimberley dioecious clade” in Australia and differs from other species in the group in its spreading decumbent habit and conspicuously prickly male floral rachis. The species is so far known from one site in Judbarra/Gregory National Park in the Northern Territory. Ex situ crosses and confirmation of inaperturate pollen grains produced in morphologically cosexual flowers indicate that these flowers are functionally female and the species is functionally dioecious. The scientific name reflects the ladder-like appearance of the inflorescence rachis armature of male individuals, the stone staircase that provides access to the type locality at the Escarpment Lookout Walk, and the importance of maintaining equitable and safe access to outdoor spaces. The common name Garrarnawun Bush Tomato is proposed in recognition of the lookout point at this site, a traditional meeting place of the Wardaman and Nungali-Ngaliwurru peoples whose lands overlap in this area.

A bush tomato that has evaded classification by solanologists for decades has been identified and is described as a new species belonging to the Australian “Solanum dioicum group” of the Ord Victoria Plain biogeographic region in the monsoon tropics of the Northern Territory. Although now recognised to be andromonoecious, S. plastisexum Martine & McDonnell, sp. nov. exhibits multiple reproductive phenotypes, with solitary perfect flowers, a few staminate flowers or with cymes composed of a basal hermaphrodite and an extended rachis of several to many staminate flowers. When in fruit, the distal rachis may abcise and drop. A member of Solanum subgenus Leptostemonum, Solanum plastisexum is allied to the S. eburneum Symon species group. Morphometric analyses presented here reveal that S. plastisexum differs statistically from all of its closest relatives including S. eburneum, S. diversiflorum F. Meull., S. jobsonii Martine, J.Cantley & L.M.Lacey, S. succosum A.R.Bean & Albr. and S. watneyi Martine & Frawley in both reproductive and vegetative characters. We present evidence supporting the recognition of S. plastisexum as a distinctive entity, a description of the species, representative photographs, a map showing the distribution of members of the S. eburneum species group and a key to the andromonoecious Solanum species of the Northern Territory of Australia. This new species is apparently labile in its reproductive expression, lending to its epithet, and is a model for the sort of sexual fluidity that is present throughout the plant kingdom.