Taxonomic turmoil down-under: recent developments in Australian orchid systematics

Abstract

Background: The issue of determining the most appropriate rank for each accepted taxon fuels ongoing controversy throughout systematics. The particularly marked escalation of such issues in modern Australian orchid systematics merits examination, not only because of wider implications in taxonomy but also because of direct effects on studies of comparative biology and conservation management.

Scope: This paper briefly reviews the causes of recent taxonomic turmoil for Australian orchids and outlines new research opportunities and conservation implications arising from an improved understanding of their molecular phylogenetics.

Conclusions: DNA sequencing and intensified field work have contributed towards a much improved understanding of Australian orchid systematics. Great progress has been made in discerning monophyletic groups or clades. Fresh interpretations of morphological evolution have been made possible by comparisons with the results of DNA analyses. Significant conceptual shifts from polymorphic species concepts to biological and phylogenetic concepts have also elevated the discovery and description of new species. Consequently, over the past decade, the number of Australian orchid species recognized by taxonomists has risen from approx. 900 to 1200. Similarly, the number of genera recognized by some taxonomists has increased from 110 to 192, resulting in 45% of Australian species/subspecies being assigned a new generic epithet since 2000. At higher taxonomic levels, much of the recent controversy in Australian orchid systematics reflects a divergence in views about where to split and assign formal names within unequivocally monophyletic groups. Differences regarding typification in the case of Caladenia have added additional confusion and complexity. However, new insights into and research opportunities concerning speciation processes in orchids have arisen from the wealth of new data and discrimination of species. Robustly supported molecular analyses of most clades enable comparative biological studies of Australian orchids to be conducted as never before. Outstanding subjects exist for exploring pollination by sexual deception and understanding the intricacies of mycorrhizal relationships and orchid conservation biology.

Fig. 1.

Molecular analysis of non-diurid orchid taxa in the subfamily Orchidoideae, illustrating genera, subtribes and tribes traditionally misplaced within Diurideae (arrowed photos). Tree 1 of eight based on combined matK and trnL-F plastid DNA sequences. Nodes that collapse in a strict consensus are indicated with solid arrows. Branch lengths are shown above the branches, and bootstrap support percentages below the branches. Percentages >83 % are shown in bold. Modified and used with permission from Kores et al. (2001). Note that some of the subtribal limits illustrated have been revised by Chase et al. (2003). Photographs (by the author unless otherwise credited): (1) Megastylis (P. Cribb); (2) Pterostylis; (3) Chloraea (C. Luer); (4) Codonorchis lessonii (A. Chapman)

Fig. 2.

Molecular analysis of the tribe Diurideae (subfamily Orchidoideae), illustrating concepts of the genus Caladenia, polyphyletic and monophyletic (solid black within vertical bars), of the following authors: (a) Brown (1810); (b) Lindley (1830–40); (c) Reichenbach (1871); (d) Bentham (1873); (e) Mueller (1882); (f) Diels and Pritzel (1905); (g) Gardner (1930); (h) George (1971); (i) Clements (1982, 1989); (j) Szlachetko (2001a); (k) Hopper and Brown (2001, 2004); (l) Jones et al. (2001). Key taxa of Caladeniinae not sampled in this analysis were the monotypic Ericksonella and Pheladenia. The arrow shows the single node that collapsed in the consensus tree at the base of the clade recognized here as subtribe Caladeniinae. Tree 1 of eight based on combined matK and trnL-F plastid DNA sequences. Branch lengths are shown above the branches; bootstrap support percentages below the branches. Percentages >83 % are shown in bold. Modified and used with permission from Kores et al. (2001). Note that some of the subtribal limits illustrated have been revised by Chase et al., 2003). Photographs (by the author unless otherwise credited) are aligned approximately opposite their position in the cladogram: (1) Cyrtostylis huegelii; (2) Caladenia flava; (3) Caladenia granitora; (4) Ericksonella saccharata; (5) Pheladenia deformis; (6) Cyanicula nikulinskyae; (7) Elythranthera emarginata; (8) Glossodia; (9) Praecoxanthus aphyllus; (10) Leptoceras menziesii; (11) Eriochilus; (12) Lyperanthus serratus; (13) Pyrorchis nigricans; (14) Leporella fimbriata (B. A. and A. G Wells).

Fig. 3.

Two systems of classification for Australian orchid genera including and allied to Caladenia and involved in recent taxonomic controversy, aligned alongside an ITS nrDNA molecular phylogeny [modified from Alcock (2005), by permission of Oxford University Press, original phylogeny from Jones et al. (2001)]. System 1 favouring a broader concept of Caladenia is that proposed by Hopper and Brown (2001, 2004a); System 2 splitting Caladenia into six genera is by Jones et al. (2001). Subgeneric names in System 1 do not align perfectly with generic names in System 2 due to dispute over typification (for details see Hopper and Brown 2004a). Generic names in brackets in System 2 are those correctly used if typification follows Hopper and Brown (2004a). Representative flowers of clades are illustrated (photographs by the author): (1) Caladenia granitora; (2) Caladenia barbarossa; (3) Caladenia filifera; (4) Caladenia flava; (5) Caladenia carnea; (6) Caladenia; (7) Cyanicula nikulinskyae; (8) Ericksonella saccharata. (9) Note the half-naked tubers in Caladenia with the daughter tubers on elongated droppers. (10) In Cyanicula, parent and daughter tubers are juxtaposed and completely encased within a multilayered fibrous tunic.

Fig. 4.

Recent discovery and naming of new species of Australian orchids due to abandonment of polymorphic species concepts in favour of more biological approaches is illustrated here with flowers of six species of Drakaea, three recently described by Hopper and Brown (2007, indicated below with *), and their sexually deceived pollinators. Flowers are of (1) D. thynniphila, (2) D. livida, (3) D. micrantha*, (4) D. glytpodon, (5) D. gracilis* and (6) D. confluens*. Inset: males of six species of thynnid wasp captured at bait flowers of Drakaea species: wasps attracted to (a) D. livida (Zaspilothynnus nigripe), (b) D. confluens (undescribed), (c) D. concolor (undescribed); (d) D. thynniphila (undescribed), (e) D. micrantha (undescribed) and (f) D. glyptodon (Zaspilothynnus trilobatus).