November’s theme was hybrids. Orchids, more than any other plant family, are likely to produce natural hybrids. Even though the overall occurrence of natural hybridisation in orchids is low, it occurs often enough to make some species identification challenging.
Hybrids mainly occur between species of the same genera such as Jenny Pauley’s Arachnorchis brumalis x A. conferta
but, less commonly, it can occur between genera as seen with Pauline Meyer’s Caladenia latifolia x A. brumalis
and her Western Australian photograph of Caladenia x enigma; a hybrid between C. falcata and Drakonorchis barbarossa.
Jones (2006) states that “Natural hybrids are more common in some genera, such as Arachnorchis, Caladenia and Diuris, than in others.” To this list could be added Thelymitra as seen with both of the winning pictures T. x truncata and T. x irregularis. Interestingly with these two hybrids, the parents are not always the same; the parents for T. irregularis could be T. ixiodies or T. juncifolia with either T. carnea or T. rubra.
A similar situation occurs with T. truncata with the parents consisting of T. juncifolia and any member of the T. pauciflora (including T. albiflora, T. arenaria, T. bracteata, T. brevifolia, T. cyanapicata, T. pauciflora) or of the T. nuda complex.
The conditions necessary for hybridisation are that the parents must grow in the same area, have overlapping flowering time and share the pollinator. Brown et al (2103) make the additional observation – Hybrids are more common between wasp and bee-pollinated species than between two wasp-pollinated species or two bee-pollinated species. … However, rare hybrids between species using the same pollination strategies, do occasionally occur …
Obviously hybridisation is more likely to occur when there is an abundance of the parent species. This situation can occur when there is mass flowering following fires or good seasonal rains. Site disturbances either through natural causes or clearing can result in increased incidence of hybridisation.
Hybrids are often infertile and will only last for the life of the individual plant but some have the ability to reproduce vegetatively and, provided the conditions remain favourable, may persist for several years.
One situation that can occur is hybrid swarm. When these occur they can make orchid identification challenging. Hybrids share the characteristic of both parents and by careful observation this can be deduced but swarms introduce an added complexity because the hybrid can backcross with either of the parents or cross fertilise with themselves. The result is a wide range of variation which makes orchid identification difficult.
Finally, some orchids will not hybridise even though the conditions are right. This could be due to specific pollinator or possibly chemical or genetic barriers.
Brown et al (2013) Field Guide to the Orchids of Western Australia, Floreat, WA, Simon Nevill Publications
Jeans, Jeffrey & Backhouse, Gary (2006) Wild Orchids of Victoria, Seaford Vic, Aquatic Photographics
Jones, David (1988) Native Orchids of Australia, Frenchs Forest, NSW, Reed Books
Jones, David (2006) A Complete Guide to Native Orchids of Australia including the Islands and Territories, Frenchs Forest, NSW, Reed New Holland
Introduction to Australian Orchidaceae CD-ROM
https://www.anbg.gov.au/cpbr/cd-keys/orchidkey/html/intro-c_hybrid.html accessed 7th December 2015
Bates, Robert (2011) South Australia’s Native Orchids NOSSA DVD Adelaide
Spotted Pink Sun Orchid – Beautiful, but Only a Hybrid
https://nossa.org.au/2014/09/26/thelymitra-x-irregularis-beautiful-but-only-a-hybrid/ accessed 7th December 2015