Inflorescence racemose, 1–many-flowered, terminal; flowers resupinate. Sepals and lateral petals free, similar. Labellum free, attached at base of column, usually similar to other tepals but sometimes slightly broader or narrower; lamina not lobed, unornamented. Column lacking free filament and style, stubby; column wings fused to (and surrounding) column, forming a mitra; dorsal part of mitra producing a sculptured, tripartite apex that in most species consists of a flat midlobe flanked by two lateral arms; basal part of mitra usually forming a low, unornamented rim in front of the stigma. Column foot absent. Anther erect, parallel to the axis of the column, persistent. Pollinia 2, soft and mealy. Stigma entire. Rostellum ventral.
Physical size, mitra sculpturing and colour intensity vary within some species owing to a gradation between showy open-pollinated and cryptic self-pollinated populations or individuals. The records of T. chasmogana R. S. Rogers and T. luteocilium Fitzg.are not substantiated for N.S.W. Some species, particularly Thelymitra ixioides hybridise readily and several species names apply to progeny resulting from sporadic, or stabilised, hybrids.
| | Key to the species | |
| 1 | Lateral arms of mitra with cilia or hair tufts; mitra midlobe large enough to conceal most or all of the anther | 2 |
| Lateral arms glabrous (arms obscure bumps or flattened fins with toothed to warty margins); mitra midlobe too small (reduced to a sheath or ornamented collar) to conceal the anther (The species in this group are sometimes treated as the variable species complex Thelymitra longifolia J. R. Forst. & G. Forst. s. lat.) | 16 |
| 2 | Mitra midlobe expansive or inflated forming a tubular, weakly ornamented, hood; hood shaped like a cone, crescent or pincer | 3 |
| Mitra midlobe short, forming an ornate crest; crest either flanked by 2 lobes or culminating in a continuous, wrinkled ridge
Back to 1 | 10 |
| 3 | Mitra midlobe with irregular ridges, bumps or warts, the hood tip short to narrow (abrupt); dorsal sepal and lateral petals often spotted | Thelymitra truncata |
| Mitra midlobe sides smooth to minutely papillose, the tip long and inflated to rounded; dorsal sepal and lateral petals never spotted
Back to 2 | 4 |
| 4 | Perianth segments overlapping widely and untidily; midlobe much elongated, flat-topped and slanted | Thelymitra megcalyptra |
| Perianth segments without severe, untidy overlap; midlobe not much elongated round-topped to dome-like
Back to 3 | 5 |
| 5 | Lateral sepals narrower than dorsal sepal, petals spotted, broader to rounder than the dorsal sepal; confined to subalpine woods | Thelymitra x simulata |
| Lateral sepals similar to dorsal sepal, petals spotless and similar to dorsal sepal; not confined to subalpine woods
Back to 4 | 6 |
| 6 | Perianth segments less than 11 mm long, opening tardily; labellum often smaller than the other 5 segments | Thelymitra pauciflora |
| Perianth segments 15–20 mm long, opening readily; labellum not smaller than the other 5 segments
Back to 5 | 7 |
| 7 | Midlobe tip narrowed, slender, notch toothed, the hairs on lateral arms confined to dense tufts terminating each arm tip; inflorescence to 80 cm high | 8 |
| Midlobe tip broadened, rounded, cleft smooth to bumpy, the hairs on lateral arms emergent along arm margins (ciliate); inflorescence to 65 cm high
Back to 6 | 9 |
| 8 | Lateral arms ending in white to yellowish tufts | 22 |
| Lateral arms ending in mauve tufts
Back to 7 | Thelymitra malvina |
| 9 | Leaf thin and shallow, flaccid; hair tuft at tip of lateral arm compact, globose; perianth usually mauve | Thelymitra fragrans |
| Leaf thick and ribbed, erect; hair tuft at tip of lateral arm looser, brushy; perianth usually blue
Back to 7 | 24 |
| 10 | Each lateral arm isolated from the ornate crest by a separate, obtrusive, colourful, accessory lobe (lobe flat to erect, columnar or wing-like, often ornamented) | 11 |
| Lateral arms not conspicuously separated from the ornate crest by abrupt lobes as the crest is an extended, exaggerated-angled ridge formed by the continuous fusion of the accessory lobes to the crest
Back to 2 | 15 |
| 11 | Lateral arms flat-fleshy, warty to papillose (bear paw); hairs coarse, forming a thick, fan-like fringe | Thelymitra x irregularis |
| Lateral arms narrow stalks, non-papillose; hairs fine forming tufted tips or clothing stalks in loose brushes
Back to 10 | 12 |
| 12 | Accessory lobes lying flat against the anther, margins deeply fringed with long finely curved teeth; base of the mitra rim bordering the stigma often with a stalked, brushy tuft | Thelymitra circumsepta |
| Accessory lobes held erect, margins lacking deep fringes or long teeth; base of the mitra rim always naked
Back to 11 | 13 |
| 13 | Crest with few rows of short calli (subtended by a dark band), lobes short, narrow and ridgelike (usually broader than long); inflorescence to 90 cm high | Thelymitra media |
| Crest with many rows of long calli (band absent), lobes long, thick and column-like (usually longer than broad); inflorescence to 60 cm high
Back to 12 | 14 |
| 14 | Perianth segments to 22 mm long and 12 mm wide (sometimes elongated); dorsal sepal and lateral petals usually spotted, never purple | Thelymitra ixioides |
| Perianth segments less than 15 mm long and 7 mm wide (never elongated); dorsal sepal and lateral petals purple, not spotted
Back to 13 | Thelymitra purpurata |
| 15 | Midlobe ridge discontinuous (with a low, notched central gap) with the ridge ends forming obliquely flaring, scalloped wings; crest ornaments usually prominent and congested | Thelymitra x merraniae |
| Midlobe ridge continuous with the ridge curving into a short, abruptly angled cone or cylinder; crest ornaments reduced and sparse
Back to 10 | Thelymitra x truncata |
| 16 | Lateral arms of mitra severely reduced to 2 rounded bumps; petals and sepals pale yellow | Thelymitra flexuosa |
| Lateral arms of mitra longer; petals and sepals mostly shades of blue, rarely yellow
Back to 1 | 17 |
| 17 | Bluish flowers with lateral petals and labellum outlined by dark veins (sepals and petals usually more than 15 mm long), lateral arms thin and narrowing; restricted to montane or subalpine sites | 18 |
| Pinkish red to cream or yellow flowers with lateral petals and labellum lacking dark veins (sepals and lateral petals usually less than 10 mm long), lateral arms thicker, often broadening; not restricted to montane or subalpine sites
Back to 16 | 21 |
| 18 | Midlobe a short, thickened rim, marginally toothed with a short, flattened to slanted notch (lateral arms held stiff and straight, strongly toothed or fringed); labellum similar to lateral petals | Thelymitra pulchella |
| Midlobe a thin or obscure sheath, lacking teeth or a flattened to slanted notch (lateral arms often coiled to spiralling, weakly toothed to lobed or entire); labellum usually broader, more concave and/or crisped than the lateral petals
Back to 17 | 19 |
| 19 | Lateral column lobes plane, crossed infront of column, apices usually in close contact. Post-anther lobe with rugulose dorsal surface | Thelymitra incurva |
| Lateral column arms curled, crossed infront of column or not, apices not in close contact. Post anther lobe surface smooth or with beady glands
Back to 18 | 20 |
| 20 | Perianth segments to 16 mm long and 10 mm wide; lateral arms short, apices often lobed | Thelymitra cyanea |
| Perianth segments to 25 mm long and 12 mm wide; lateral arms longer, apices entire
Back to 19 | Thelymitra venosa |
| 21 | Petals and sepals usually less than 8 mm long, sepal tips blunted or ending in very short points; margins of lateral arms scalloped but poorly ornamented to weakly papillose | Thelymitra carnea |
| Petals and sepals usually more than 8 mm long, sepal tips acute and ending in long, fine, points (often curved); margins of the lateral arms densely but irregularly fringed with slender to warty teeth
Back to 17 | Thelymitra rubra |
| 22 | Perianth segments <20 mm long; flowers opening tardily; plant moderately robust, to 60 cm tall | 23 |
| Perianth segments >20 mm long for at least somes flowers in larger individuals; flowers opening freely; plants often very robust, to 100 cm tall
Back to 8 | Thelymitra aristata |
| 23 | Anther inserted well above base of column at anthesis, not or only partially obscured behind the stigma. Post-anther lobe slightly hooded | Thelymitra adorata |
| Anther inserted at base of column at anthesis, mostly obscured behind the stigma. Post-anther lobe flat
Back to 22 | Thelymitra kangaloonica |
| 24 | Perianth segments rarely exceeding 18 mm long. Post-anther lobe emarginate or with a V-shaped notch at apex | Thelymitra nuda |
| Perianth segments 15–20 mm or up to 25 mm long. Post-anther lobe irregularly bilobed, distal margin irregularly toothed and usually with two prominent forward-pointing horn-like teeth
Back to 9 | Thelymitra alpina |
