Citation: Forster & Forster f., Char. Gen. Pl. 97:t. 49 (1776).

Derivation: Greek thelys, feminine; mitra, a turban; referring to the hood of the column in several species.

Synonymy: Not Applicable

Common name: Sun-orchids.

Description:
Plants terrestrial, glabrous, very rarely with hairy leaves; tubers ovoid, new one produced at the base of the parent plant; leaf solitary, sheathing at the base, linear to lanceolate, rarely ovate-lanceolate or terete, generally much elongated and fluted, often thick and fleshy; cauline bracts 1 or 2, leafy; floral bracts large, usually exceeding the ovary.

Raceme usually of few to 20 resupinate flowers, rarely flower solitary; perianth glabrous, usually opening widely in the sun, colourful, albino forms not infrequent; dorsal sepal uppermost, similar to the lateral sepals and petals, the labellum undifferentiated from the others in colour, sometimes differing slightly in shape; column erect, widely winged; wings joined in front at the base and variously lobed and ornamented at the sides (e.g. fig. 998) commonly produced behind and over the anther so as to form a more or less complete often 2-lobed hood which is entire or plumed or decorated with various excrescences; anther 2-celled, erect or folded inwards, usually partly or wholly hidden by wings, its connective often produced into an appendage (anther point) which may be short or long, entire or 2-fid; pollinia 2 per cell, each deeply 2-lobed or in pairs, attached directly or by means of a short caudicle to the disk of the rostellum or sometimes quite unconnected with it; pollen mealy or finely granular; stigma borne on an erect plate-like style either in front or the anther more or less concealing it or below the anther, cleft on top to varying degrees; viscid disk well developed and situated in a slot or a depression in the upper border of the stigma; rostellum small and narrow.

Distribution:  About 45 species mostly Australian, extending also to Indonesia, the Philippines and New Caledonia, with 12 species in New Zealand of which 7 also occur in South Australia.

Biology: Most South Australian species are self-pollinated but bees are effective pollen vectors on all species. The column offers the best characters for identifying species, though habitat, leaf form, shape and colour of perianth-segments are also useful. For purpose of description the structures associated with the column and included in the general term "wings" are treated as follows (fig. 998):- Column-arm: (lateral lobes) is applied to 2 small processes, one on each side of the anther, and each supplied by a single unbranched vascular bundle; these are thought to represent staminodes. They are of different forms: (a) ribbon-like to more or less thickened and clavate, plain or ornamented with teeth or tubercles; (b) each consisting of a more or less terete stem bearing on the sides, back and top numerous hair-tufts (cilia), hair-like structures I or 2 cells wide, throughout their length; (c) the stem partly to quite flattened, bearing on its lower margins teeth, laciniae or fimbriae which are relatively few, mostly several cells wide at their bases and tapering to their tips, the top of such column-arms sometimes occupied by more cilia-like structures. Post-anther lobe (mid-lobe) lies between the column-arms and mostly behind the anther; it has a more or less complex vascular supply, always closely associated with that of the functional anther, and may be thought of as an outgrowth of the filament. In a few species (e.g.T. venosa) it is represented only by a band of small calli crowded across the back of the anther; in most species it stands erect with a free margin and may be short or tall, plain or ornamented with fleshy tubercles, truncate or cucullate, and is often distinctively coloured. At its maximum development the post-anther lobe forms a somewhat fleshy, well-vasculated hood that overhangs and quite hides the anther (e.g. fig. 1006B). Side lobule (adjacent divisions) stands in a few species immediately behind the column-arm and is more or less distinct from the middle part of the post-anther lobe (e.g. fig. 1000A); it tends to be fleshy with irregularly jagged margins and occasionally sharp surface tubercles, but it includes no vascular strand. Species with distinct side lobules have sometimes been described as having a 3-partite mid-lobe.

Taxonomic notes: Some specimens can not be identified with any certainty as many of the species are very variable. (The above discussion of terminology is adapted from L. B. Moore & E. Edgar (1970)).

Key to Species:

1. Leaf spirally twisted round the scape or flexuose	T. matthewsii 14.
1. Leaf straight
2. Leaf less than 4 times as long as wide; flowers yellow-green blotched brown	T. fuscolutea 8.
2. Leaf more than 5 times as long as wide; flowers not blotched brown
3. Column-arms (fig. 996) with hair-tufts (cilia, fimbria)
4. Hair-tuffs yellow or cream-coloured
5. Post-anther lobe produced into a fleshy hood over the anther
6. Flowers pink, opening freely; post-anther lobe with shallowly cleft smooth entire margins, pollinia intact above the distinct viscidium	T. chasmogama 5.
6. Flowers bright-blue, opening in warm sunshine; post-anther lobe with deeply cleft involute margins, pollinia collapsing over the indistinct viscidium	T. holmesii 9.
5. Post-anther lobe not produced into a fleshy hood over the anther
7. Perianth-segments spotted
8. Flowers a bright rose-pink, expanding freely; post-anther lobe denticulate, short, abrupt; hair-tufts bright-yellow	T. irregularis 10.
8. Flowers lilac-blue, opening in warm sunshine; post-anther lobe produced into 2 bright-yellow entire wings; hair-tufts cream-coloured with red tints at the base .	T. merranae 15.
7. Perianth-segments not spotted
9. Anther-lobes smooth, cloven-like V expanded over the anther like 2 shell-like lobes; with a mould-like bloom	T. mucida 16.
9. Anther-lobes crested or dentate not expanded over anther
10. Flower pinkish or light-red, rarely yellow; post-anther lobe higher than minute side-lobes	T. luteocilium 12.
10. Flower blue; the side-lobules, oblong and higher than the post-anther lobe	T. retecta 19.
4. Hair-tufts white or pink, drying brown
11. Column consisting of a post-anther lobe and 2 column-arms
12. Post-anther lobe truncate; flowers spotted	T. x truncata 21.
12. Post-anther lobe apex usually swollen, not truncate; notched or denticulate; flowers not spotted
13. Apex of post-anther lobe denticulate or fimbriate; leaf widely lanceolate with a fleshy leaf-like bract above it	T. aristata 2.
13. Apex of post-anther lobe entire or notched; leaf lanceolate, without a fleshy leaf-like bract above it
14. Post-anther lobe 2-fid with involute margins; sepals grey outside; leaf deeply channelled	T. holmesii 9.
14. Post-anther lobe notched or almost entire; sepals blue, pink or brown outside; leaf shallowly channelled
15. Flowers less than 15 mm diam.; post-anther lobe slightly inflated; the hair-tufts usually not very dense and held vertically; pollinia collapsed onto the stigma (the flower opening only in very hot and humid weather)	T. pauciflora 18.
15. Flower more than 15 mm diam.; post-anther lobe usually much inflated; the hair-tufts dense, somewhat horizontal or angled out in front of the column; pollinia remaining intact, with a large viscidium (the flowers opening freely in warm or sunny weather)	T. nuda 17.
11. Column consisting of a post-anther lobe, 2 side-lobules and 2 column-arms
16. Leaf more than 15 mm wide	T. epipactoides 6.
16. Leaf less than 10 mm wide
17. Perianth-segments spotted	T. ixioides 11.
17. Perianth-segments not spotted	T. canaliculata 3.
3. Column-arms without hair-tufts (fig. 998A)
18. Column-arms rudimentary or absent; anther-point large oblong and protruding	T. flexuosa 7.
18. Column-arms produced into a distinct appendage; anther-point various
19. Column-arms ribbon-like, erect, more or less spirally twisted inwards; anther-point prominent, ending in 2 horn-like points	T. venosa 22.
19. Column-arms fleshy, suberect; anther-point prominent, obtuse
20. Column-arms less than 3 mm long, in front of the column apex, crenate or rugulose-denticulate; post-anther lobe prominent, crenulate
21. Column-arms marginally crenate, more than twice as long as wide; post-anther lobe almost as high as the anther; flowers less than 8 mm diam	T. carnea 4.
21. Column-arms rugulose-denticulate, less than twice as long as wide; post-anther lobe rather higher than the anther; flowers crimson, more than 8 mm diam.	T. rubra 20.
20. Column-arms more than 3 mm long, held above the column; post-anther lobe lacking or replaced by a deep sinus and side lobules
22. Column-arms smooth, not ciliate, reddish-brown, (like rabbit-ears); flowers yellow	T. antennifera 1.
22. Column-arms crenulate to rugulose, ciliate, yellow to pink; flowers salmon-pink or reddish often with yellow borders	T. macmillanii 13.

Author: Not yet available