Cryptic species in an ancient flowering‐plant lineage (Hydatellaceae, Nymphaeales) revealed by molecular and micromorphological data

Abstract

The flora of the southwestern Australian biodiversity hotspot is rich in endemic species, many of which remain to be discovered or properly described; estimates of species diversity and levels of endemism should take into account the possible occurrence of cryptic species. Here we explore taxonomic diversity in a Western Australian lineage belonging to the primarily Australian genus Trithuria, the sole genus of Hydatellaceae (Nymphaeales). Recent molecular evidence supports the existence of cryptic species in self-pollinating members of section Trithuria. We investigate Western Australian plants currently classified as T. australis s.l., a selfpollinating member of the section Hydatella. Using evidence from microsatellite data (SSRs), an expanded molecular phylogenetic analysis based on four plastid markers, and fruit micromorphology, we suggest that material traditionally classified as T. australis s.l. belongs to at least four species. Two species occur in the northern part of the distribution range of the group (31°S to 33°27′ S), and two in the southern part (33°27′ S to 35°S). Each northern species has distinctive fruit micromorphology not recorded in other members of the genus. The two southern species are well characterized by molecular characters and seem to be allopatric, but lack obvious morphological differences from each other. We describe one of the northern species as T. fitzgeraldii sp. nov. However, clarifying the names of the other three species is currently problematic as T. australis and another available name are based on collections made 117 years ago, from localities distant from any subsequent records of Hydatellaceae. Based on genome size estimations, we also demonstrate two ploidy levels in the T. australis complex. Our study supports the view that species diversity in Hydatellaceae is strongly underestimated.

Why the Monophyly of Nymphaeaceae Currently Remains Indeterminate: An Assessment Based on Gene-Wise Plastid Phylogenomics

“…For example, the inclusion of one representative of each of the four sections of the genus Trithuria could be included in future investigations in order minimize the level of homoplasy between the divergent family of Hydatellaceae and the rest of the plant order. Such an inclusion would also benefit the ongoing evaluation of the species diversity of Hydatellaceae, which was recently reported as strongly underestimated [58].…”

Trithuria brevistyla (Hydatellaceae), a new combination for the New Zealand endemic species from the South Island

“…In their new article Sokoloff et al (2019) reported the existence of cryptic species among self-pollinating members of Trithuria sect. Trithuria and sect.…”

“…In particular, they demonstrated, using evidence from microsatellite data (SSRs), an expanded molecular phylogenetic analysis, and fruit micromorphology, that Western Australian plants currently classified as T. australis sensu lato (sect. Hydatella) in fact belong to at least four species; of those four newly detected entities, one was formally described as a new species, Sokoloff et al (2019) concluded that species diversity in Hydatellaceae is strongly underestimated. These findings are well in line with our proposed treatment of the South Island Trithuria as a distinct species.…”

“…f. (Hydatellaceae U.Hamann) is a genus of ca. 12 currently recognized species, or probably 15 or more species, as new data on cryptic taxa suggest (Sokoloff et al, 2019). At least eleven (or more) of these occur in Australasia, with one species, T. konkanensis S.R.Yadav & Janarth., being endemic to India (Yadav & Janarthanam, 1994, 1995Sokoloff et al, 2008Sokoloff et al, , 2011Iles et al, 2012).…”

“…ex Bercht. & J.Presl, among the early-branching lineages of angiosperms, stimulated much interest of researchers and resulted in numerous important publications on morphology, anatomy, genetics, phylogeny, evolution, biogeography, and other aspects of these plants (see overviews and relevant references in Sokoloff et al, 2011Sokoloff et al, , 2019Smissen et al, 2019;etc.). A new infrageneric system of Trithuria (incl.…”