Systematic studies on Thysanotus R.Br. (Asparagales: Laxmanniaceae).

Abstract

Thysanotus R.Br. (Asparagales; Laxmanniaceae) is a genus native to Australia with c. 50 species distributed chiefly in Australia. To date, Thysanotus lacks proper and detailed systematic studies based on molecular and/or non-molecular data. Therefore, carrying out a detailed systematic study using molecular and/or non-molecular data seemed important. Furthermore, generic placement of Murchisonia Brittan has always been controversial and this placement required testing under a phylogenetic framework. The generic relationships within Laxmanniaceae/Lomandraceae are considered uncertain; therefore, a phylogenetic analysis using molecular and morphological data is necessary to properly understand the generic relationships of Laxmanniaceae. Detailed studies on stem anatomy and morphology were carried out in order to understand the systematic significance and phylogenetic signal of these characters. The cp DNA (trnL intron and trnL–F intergenic spacer) and nuclear ITS2 gene regions were amplified and the results compared and combined with a morphological analysis. Phylogenetic analyses were carried out using Arthropodium R.Br and Eustrephus R.Br as outgroup taxa. There was sufficient variation in general morphology, seed micromorphology and stem anatomy and were potentially useful in understanding phylogenetic relationships of Thysanotus. A number of synapomorphies based on general morphology and stem anatomy such as absence of pendent flowers and absence of irregular shaped epidermal cells were recognised. The molecular data and the combined data yielded highly resolved consensus trees and enabled us to recognise three main lineages within the genus, each representing life history adaptations. Murchisonia was consistently nested within Thysanotus in all analyses showing a need for the return of both species to Thysanotus. Insights to intraspecific variation were also discernable from morphological, molecular and the combined analyses in species such as T. patersonii and T. juncifolius. Two new Thysanotus species, T. unicupensis and T. racemoides are also described. Our data strongly support the current circumscription of Laxmanniaceae, but suggest that there are three main lineages within the family, rather than the two previously recognised subfamilies.