Morphology and the earliest-known herbarium specimen of Solanumplastisexum. A Flowering stem with a single staminate flower in 2016 B Mature fruit C Erect inflorescences bearing staminate flowers in 2018 and D Specimen collected by P. Latz in 1974, held at DNA and annotated by D. Symon with an annotation indicating his confusion about the reproductive morphology of the specimen (male rachis visible above fruit on far left).
As one of the most species-rich angiosperm genera (Frodin 2004), Solanum L. is also fast growing, with more than 90 species described within the last decade alone (e.g. Gouvêa et al. 2019; Gouvêa et al. 2018; Agra 2008; Stehmann and Moreira 2016). Members of the genus occupy all continents except Antarctica and inhabit diverse niches. The “spiny solanums,” SolanumsubgenusLeptostemonum (Dunal) Bitter, make up the largest lineage (ca. 450 spp.) within the genus and have been the subject of much recent work related to their evolution, diversity and natural history (e.g. Bohs 2005; Levin et al. 2006; Anderson et al. 2007; Stern et al. 2011; Särkinen et al. 2013; Vorontsova et al. 2013; Vorontsova and Knapp 2016; Knapp et al. 2017; Aubriot et al. 2016; Martine et al. 2019).
The spiny solanums appear to have arrived in Australia some time in the last 5–10 million years (Särkinen et al. 2013) and have continued to radiate throughout the continent with a large portion of the currently known species diversity occurring in the upper third of the continent known as the Australian Monsoon Tropics (AMT) (Bean 2004). While this radiation is reflected in diverse plant morphologies (e.g. foliage, armature, trichomes/indument, growth form, seasonal habit), the most interesting variety in form may be related to reproductive biology (Symon 1970; Symon 1979a; Symon 1979b; Symon, 1981; Anderson and Symon 1988; Anderson and Symon 1989; Martine and Anderson 2007). In particular, the spiny solanums of the AMT exhibit three primary breeding systems (breeding system used here sensuNeal and Anderson 2005): 1) hermaphroditic species with perfect flowers (i.e. S.quadriloculatum F.Muell. and approximately 10 other species), 2) cryptically dioecious species that bear functional pollen and functional gynoecia on separate individuals (i.e. S.dioicum W.Fitzg. and approximately 12 other species) and 3) andromonoecious species with inflorescences bearing one perfect flower at the base of each inflorescence and several to many staminate flowers above it (i.e. S.chippendalei Symon and about 13 other species). Our research team has recently been interested in the evolution of the andromonoecious taxa and, through field and population-level genomic study (in prep), has recognised a new species that is evolutionarily and morphologically distinctive.
The new taxon is the latest in a series of novelties from a set of taxa and forms within the “andromonoecious bush tomato” clade (Martine et al. 2006; Martine et al. 2009) recently described from the region (e.g. Bean and Albrecht 2008; Martine et al. 2016; Lacey et al. 2017) and part of a larger lineage of andromonoecious, hermaphrodite and functionally dioecious species in the “S.dioicum + S.echinatum Group” (sensuMartine et al. 2019). Across the southern margin of the AMT, where many of these taxa are distributed, mosaic habitats and corresponding environmental pressures, coupled with climatic fluctuations over the last two million years (Bowman et al. 2010), appear to have driven speciation within Solanum and other plant lineages of the region (Edwards et al. 2017; Edwards et al. 2018; Jobson et al. in prep; Martine et al. unpublished data).
In this paper, we describe Solanumplastisexum Martine & McDonnell, sp. nov., a new species restricted to a small area in the central region of the Northern Territory of Australia that has confounded field botanists since at least the early 1970s. The few historical collections made of this taxon were especially confusing to Solanum experts (Fig. (Fig.1)1) because plants may lack staminate flowers and/or the upper staminate rachis (typical for andromonoecious species) and it is often deciduous at fruit maturity. Recognition of this new species is supported by a suite of morphological characters including the lack of lobing on the leaves, a small apical leaf size and long-triangular calyx lobes on the staminate flowers. We include a morphometric comparison amongst closely-allied taxa, representative photographs, a distribution map and a key to the andromonoecious taxa of the Northern Territory along with the description of the new species.
Closely related species of andromonoecious bush tomatoes included in this study. ASolanumjobsoniiBS.watneyiCS.succosumDS.plastisexumES.diversiflorum and FS.eburneum. Colours associated with each taxon also used in Figs Figs3,3, ,44.
Abstract: 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 “Solanumdioicum 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 SolanumsubgenusLeptostemonum, Solanumplastisexum 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.
Keywords: New species, andromonoecy, Solanaceae , Leptostemonum
More at this link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6592974/