Abstract
We found several specimens of Tropidia connata, a mycoheterotrophic orchid from Borneo, with features which have never been described in any of the existing literature, namely subterranean tubers. We mainly focus on the importance of the subterranean structures in comparison with the mycoheterotrophic genus Kalimantanorchis from the tribe Tropidieae. This finding of the tuberous structure gives a new insight into the classification of mycoheterotrohic species of Tropidieae and might affect the generic placement of Kalimantanorchis. We made a detailed study on the newly discovered specimens as well as the type, and found more diagnostic characters of T. connata than the previous description. Considering that the type specimen lacks the whole tuberous character, we consequently designate an epitype with a drawing and emend the description.
Highlights
The genus Tropidia Lindl. (Orchidaceae, Epidendroideae, Tropidieae) currently contains about 30 species mainly distributed from Far East Asia, India, Sri Lanka, Indochina, Malaysia, Indonesia, the Philippines and New Guinea to northern Australia, spreading across the South Pacific Islands
The presence of underground tubers has never been described in the genus Tropidia, it was described for Kalimantanorchis nagamasui Tsukaya, M.Nakaj. & H.Okada (Tsukaya et al 2011)
In addition to the tuberous structure, we found an abscission layer on bracts and two fibrous protrusions attached to the adaxial side of the stigma, both of which have never been described for other mycoheterotrophic Tropidieae species
Summary
The genus Tropidia Lindl. (Orchidaceae, Epidendroideae, Tropidieae) currently contains about 30 species mainly distributed from Far East Asia, India, Sri Lanka, Indochina, Malaysia, Indonesia, the Philippines and New Guinea to northern Australia, spreading across the South Pacific Islands. Due to the rare occurrence of the mycoheterotrophic species in general and to the difficulty in extracting a complete root system, the subterranean parts of most mycoheterotrophic plants are less known than their aerial parts (Imhof et al 2013). This is the case for Tropidia connata, with no description provided for its subterranean parts (Wood and Cribb 1994). We provide an emended description of this enigmatic species, T. connata
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