Petalochilus – when use of a segregate or common name is helpful

The following article is from the Native Orchid Society of South Australia Journal Volume 44 No 7, author Rosalie Lawrence.

Over the years there have been many orchid name changes (particularly at genus level), some quite drastic, some multiple times and for many there can be a reversion back. Yes, this creates confusion but there are times when some of these name changes, known as segregates (both at species and genus level) can be useful.

Caladenia carnea (synonym Petalochilus carneus) Photographer Lindsay Ames

A case in point, is Lindsay Ames’ winning photograph (June) – Caladenia carnea synonym Petalochilus carneus. Petalochilus was proposed as a genus in 2001 by DL Jones, MA Clements, et al. It was one of many proposed genera changes. Many discussion papers followed but in 2015 after further taxonomic and DNA work, Mark Clements et al published a paper that “points to Lindley’s 1840 interpretation of Caladenia (…..) as being the most accurate reflection of the group.” Hence the discontinued use of Petalochilus and the other segregate genera.

So, it currently belongs with Caladenia, a large genus with over 350 species (mainly in Australia). It is a genus with great morphological (visual) diversity – compare Caladenia tentaculata with C. cucullata or C. flava. But Caladenia
subgenera Caladenia (synonym Petalochilus*), as a much smaller segregate genus allows us to visualize a specific group within the Caladenia genus.

Caladenia flava Photographer Pauline Meyer

Caladenia sens. lat. are characterised by single hairy leaf, lacking lobes or serrations; hairy stem; showy flowers with similar sepals & petals. The labellum is highly modified consisting of three lobes with calli on the middle lobe.

Caladenia tentaculata (synonym Arachnorchis tentaculata) Photographer Jane Higgs

Petalochilus is further characterised by small (1 – 5 cm) pink to white flowers,
short broad forward projecting tepals; erect to slightly incurved dorsal sepal,
distinct trilobe labellum, hinged, with calli and red transverse bars, column
green to pink with red to purple bars.

Caladenia carnea (synonym Petalochilus carneus) Photographer: Rob Pauley

Yet within Petalochilus itself there can be further groupings of which P carneus is most likely the main one. This consists of at least 8 species – P carneus (C carnea), P catenatus (C catenata), P coactilis (C coactilis), P fuscatus (C fuscata), P ornatus (C ornata), P prolatus (C prolata) , P. vulgaris (C vulgaris) and P xantholeucus (C xantholeuca). When a specimen cannot be identified to species level, it may be helpful to refer to it as a complex.

This is where comes the fun of trying to identify the specific species in the field (or for that matter from a photograph). To help myself understand, I often produce comparison charts based on descriptions found in the literature. The chart comparing the eight species is available as a pdf.

Caladenia prolata (Petalochilus prolatus) Photographer: Helen Lawrence

*Throughout the article the synonym Petalochilus is used for Caladenia subgenera Caladenia to make a clear distinction from Caladenia sens lat. It needs
to be noted C carnea is considered the type specimen for Caladenia so with any splits, it will remain in Caladenia.

References

Backhouse G et al,Bush Gems: a guide to the Wild Orchids of Victoria 2016
Bates R B South Australia’s Native Orchids 2011
Clements MA, et al, Caladenia Revisited: Results of Molecular Phylogenetic Analyses of Caladeniinae Plastid and Nuclear Loci 2015
Jones DJ, A Complete Guide to Australian Orchids including it Territories and Islands 2006
https://en.wikipedia.org/wiki/Caladenia Accessed 3 August 2020
https://www.pacificbulbsociety.org/pbswiki/index.php/Petalochilus Accessed 3 August 2020

Thank you to Andrew Brown for reviewing this article.