Pandanales

Stemona aphylla (Stemonaceae) was rather recently recognized by us as a candidate for being mycoheterotrophic. Graib (1912) noted “foliis ad bracteas squamoideas reductis” in his original description of the species, but made no record of its color. However, Stephen Pyne and Araya Jatisatienr, co-authors of a phytochemistry paper on that species (Mungkornasawakul et al. 2009), told me that S. aphylla has green leaves and a recent publication on the Stemona of Thailand (Inthachub et al. 2010) explained the confusion by two growth forms of S. aphylla, S. involuta and S. phyllantha, a precocious flowering of an upright stem with only scale leaves in contrast to a twinging and leafy growth mode. It, thus, does not belong to our list. Nevertheless, further research on its mycorrhiza is highly recommended because 1. nothing is known on the anatomy and possible mycorrhiza of the interesting tuberous root system, 2. there may be partial mycoheterotrophy due to the dual growth mode similar to the case in Pyrola aphylla/stricta, and 3. Stemonaceae are closely related to the clearly mycoheterotrophic Triuridaceae.
Stemonaceae are placed quite securely in the Pandanales which inlcude the Triuridaceae, but intraordinal phylogeny is still unclear (Chase et al. 1995, 2000, Caddick et al. 2002, Davis et al. 2004). In a morphological cladistic study Rudall and Bateman (2006) suggest that Stemonaceae are paraphyletic and include the Triuridaceae.