Rhizanthella speciosa M.A.Clem. & D.L.Jones APNI*
Description: Terrestrial, subterranean, saprophytic herb with fleshy underground stem, not observed but probably similar to Rhizanthella slateri.
Inflorescence bracteate, flower-bearing portion compressed into a globose capitulum 15–30 mm diameter, surrounded by 16–18 imbricate, fleshy, triangular-ovate sheathing bracts 10–12 mm long by 3–4 mm wide; bearing 15–35 flowers, each subtended by a fleshy, translucent, triangular floral bract 16 mm long and 7 mm wide with an acute apex. Flowers widely opening, 5 mm wide and 9–11 mm long, dorsal sepal triangular-ovate, base truncate, apex acuminate, 10 mm long by 4–5 mm wide when flattened (dimensions from Fig. 1 b,c,j in Clements and Jones 2020), outer surface rugose (Fig.1c), translucent with purple markings; lateral sepals 8 mm long by 5 mm wide, nearly deltoid or broadly triangular-ovate with a truncate base in the basal half, abruptly narrowed above into a long acuminus, translucent with purple markings; petals broad lanceolate, slightly asymmetrical and falcate, with a mid-vein, 7 mm long and 2.5 mm wide, apex tapered and acute, translucent with purple streaks. Labellum attached to the column foot by a hinged narrow claw 0.6 mm long; narrowly obcordate, broadest about midway along its length, 4 mm long by 3 mm wide, thick, fleshy, dark purple-black with paler narrow central channel extending to apex, surface and margins densely papillate, papillae in medial channel sparse, apex rounded to obtuse. Column erect, 4 mm long by 1 mm wide, translucent white with purple markings, anterior surface dark purple, apex narrowed, extending just beyond anther; column wings narrow, 0.5 mm long, flanking the anther; anther cap c. 1 mm long, without a rostrum.
Fruit, fleshy, narrowly cylindrical, pink to light maroon at maturity.
Flowering: Recorded in October and November
Distribution and occurrence: Known from Barrington Tops National Park, between 400 and 500 m elevation.
In tall wet sclerophyll forest with Eucalyptus saligna and E. microcorys, with Syncarpia glomulifera over a well developed rainforest subcanopy including Trochocarpa laurina and Synoum glandulosum, with a sparse ground layer, on dark clay loam.
NSW subdivisions: NC
Rhizanthella speciosa could only be confused with R. slateri or R. omissa, the two other Rhizanthella species currently known to occur in south-east Australia. Rhizanthella speciosa can be recognised by its 1) long sheathing bracts (16-18 mm long); 2) lateral sepals c. 10 mm long with a filiform, smooth, apex; and 3) narrowly obcordate labellum dark-purple in colour with a paler medial band extending to and including the labellum apex. Rhizanthella speciosa inflorescences emit a distinct odour, described as 'animal- or fungal-like' (Clements and Jones 2020: 224).
Text by Clements and Jones (2020) with modification by Matt A.M. Renner (31 July 2020)
Taxon concept: Clements MA, Jones DL (2020) Notes on Australasian orchids 6: a new species of Rhizanthella (Diurideae,subtribe Prasophyllinae) from eastern Australia. Lankesteriana 20: 221-227.
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