Xanthorrhoeaceae - Classification

Classification

The family Xanthorrhoeaceae has been placed into four different orders over time. According to Rudall this re-classification has been a consequence of improvement in molecular and morphological analysis. Re-classification is also a reflection of the increased emphasis on placing families within an appropriate order. Early classification of Xanthorrhoeaceae placed the family in the order Liliaceae, followed by placement in the order Agavales, alongside the family Agavaceae. Later classification by Cronquist and Beadle followed more traditional methods. This classification included Xanthorrhoeaceae within the order Liliales, under the subclass Liliidae. Cronquist had difficulty classifying the less obviously delineated Lilioid monocots; consequently, taxa from both orders Asparagales and Liliales were placed into a single family Liliaceae by Cronquist. Flora of Australia replicated Cronquist's classification, by placing ten genera within Xanthorrhoeaceae. Bedford et al. acknowledged at this time that some authors, such as Dahlgren et al. (1985), were segregating the ten genera into two or three separate families, rather than all grouped under Xanthorrhoeaceae. A review of the systematics of the group, using anatomical and molecular data has led to the conclusion that the genera Baxteria, Calectasia, Dasypogon and Kingia should be included in the family Dasypogonaceae, based on the presence of silica bodies found in the epidermal cells of these genera. They also found that Acanthocarpus, Chamaexeros, Lomandra, Romnalda and Xerolirion should be included in the family Lomandraceae, due to similar leaf anatomy. Xanthorrhoea was found to be placed correctly in Xanthorrhoeaceae, due to its isolated taxonomy. The classification of the genera contained within the group has changed in light of new molecular analysis (combined rbcL and trnL-F DNA analysis) and morphological analysis (leaf anatomy, silica within cells), as well as through reviewing previous published literature on Xanthorrhoeaceae, as carried out by researchers such as Rudall and Chase et al. The only stable classification over time has been of the genus Xanthorrhoea, which has remained within Xanthorrhoeaceae. This single genus currently contains 30 species.