Thelymitra

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Sun Orchids
Salmon Sun orchid (Thelymitra rubra) clearly showing the mitra
Salmon Sun orchid (Thelymitra rubra)
clearly showing the mitra
Plant Info
Scientific classification
Kingdom: Plantae
Division: Magnoliophyta
Class: Liliopsida
Order: Asparagales
Family: Orchidaceae
Subfamily: Orchidoideae
Tribe: Diuridiae
Subtribe: Thelymitrinae
Genus: Thelymitra
J.R.Forst. & G.Forst., 1775

Type Species
Thelymitra longifolia
J.R.Forst. & G.Forst., Char. Gen. Pl.: 49 (1775).
Species
See text.

Thelymitra is a genus of orchids known as 'sun orchids' in reference to their habit of only opening in warm weather.


Description

They are about 100 species distributed in higher rainfall areas across Australia (with 50 or so species), New Zealand (10+ endemic species), New Caledonia (2), Timor, Java, and the Philippines.

The type species is Thelymitra longifolia J.& G. Forst. 1775 from the South Island of New Zealand. The scientific name Thelymitra was given by J. R. and G. Forster, botanists on Captain Cook's second voyage. The genus name is derived from the Greek words thely (woman) and mitra (mitre hat), referring to elaborate shape of the staminodal (staminode = sterile stamen) structure at the top of the column, called a mitra.

These terrestrial orchids are only above ground during spring and early summer, usually with a single leaf, growing up from two underground tubers. It is elongated or linear-lanceolate and glabrous. The Custard Orchid (T. villosa) is the only species with a hairy leaf. The leaves of T. spiralis and T. variegata are spirally twisted.

The flower stalk is usually a bluish-green colour. The flower stem usually carries 4 to 10 flowers (even up to 20 flowers in the Plain Sun Orchid, T. holmesii), often opening all at once, though some species have only one flower each year. The flower size is between 1 and 6 cm. These flowers only open in bright sunlight (in combination with warmth and humidity), close at night and during cold or cloudy weather.

Sun orchids exhibit a particular characteristic : their lip shows, except in a few species such as T. variegata, almost the same shape, colour, colour pattern or size as the other petals and sepals. This gives a symmetrical shape to the perianth. Furthermore the lip lacks ornamentation. In other orchid genera, the lip has a distinctive shape and colour. The particular shape and color of the sun orchids mimics the flowers of lily family (Liliaceae) and the family Goodeniaceae, aiming by deceit for the same insect pollinators. The Slender Sun Orchid (T.pauciflora) only opens for a short time (or not at all) and is self-pollinating. This self-pollination is a successful strategy followed by several other species such as and T. circumsepta, T. graminea, T. holmesii and T. mucida.

Once the weather dries out the leaf shrivels away and the orchid lies as a single spherical tuber.

Sun orchids come in most colours, including purple, deep blue (T. pauciflora), white, pink, magenta, maroon, yellow (T. antennifera) and red (T. x macmillanii). Most are a single colour or have spots, a few have stronger variation and are multi-coloured. The deep blue colour, found in about 75% of the sun orchids, is of a rare kind, found only in 5 other orchid genera.

Several species are considered by the IUCN as endangered (T. epipactoides) or critically endangered (T. gregaria, T. hiemalis and T. x mackibbinii. A number of conservation measures are underway in South Australia.

Until shortly, the taxonomy of the genus was outmoded and understudied. Jeffrey A Jeanes of the Royal Botanic Gardens Melbourne has recently (2004) done a taxonomic revision, resolved several species complexes and described a considerable number of new species (see Muelleria 19; 2004)

Several Thelymitra species :2, 3, 6, 7, 8, 9

Species

Natural hybrids

  • Thelymitra × chasmogama R.S.Rogers 1927 (T. luteocilium × T. nuda)
  • Thelymitra × mackibbinii F.Muell. 1881 (T. × macmillanii × T. nuda)
  • Thelymitra × macmillanii F.Muell. 1865 (T. antennifera × T. luteocilium)
  • Thelymitra × truncata R.S.Rogers 1917


Intergeneric hybrid

  • xCalomitra (Calochilus x Thelymitra) (unplaced name)

Cultivation

Thelymitras can be grown in a freely draining, dense mixture with partially composted organic matter. A suitable mixture is an equal mix of 7 mm road screenings, year old composted wood chips and commercial potting mix. It is good practice to cover the surface in pine or she-oak needles to control water loss and to feed the mychorizal fungi that support the orchid.

Due to the flowers only opening in warm weather, it is common practice for showing them, to use a bank of strong incandescent lights to simulate the warm sun.

Some work has gone into growing hybrids for better growing and more colour. The most popular hybrid is probably Th. x "Kay Nesbitt" with its strongly coloured red-ish pink flowers.

References

  • Pamela Burns-Balogh and Peter Bernhardt (1988). "Floral evolution and phylogeny in the tribeThelymitreae (Orchidaceae: Neottioideae)". Plant Systematics and Evolution 159. 
  • Breiner, E. and Breiner, R. (2003). "Thelymitra, die sun orchids: eine bemerkenswerte Orchideen-Gattung aus Australien.". Orchidee 54 (3): 350-351.  (in German)
  • Jeans, J. A. (2004). "A revision of the Thelymitra pauciflora R.Br. (Orchidaceae) complex in Australia". Muelleria 19: 19-79. 
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