Pterostylis peakallana N.Reiter, B.Kosky & M.A.Clem., 2021

Reiter, Noushka, Kosky, William & Clements, Mark, 2021, Two new species of Pterostylis (Orchidaceae; Orchidoideae) from the Sunset Country, Victoria, Australia, Phytotaxa 500 (3), pp. 153-165 : 162-163

Pterostylis peakallana N.Reiter, B.Kosky & M.A.Clem. , spec. nov. (Fig. 7)

Type: — Australia. Victoria: Wyperfeld National Park, Brocken Bucket , 130 m, 9 Nov 2019, Reiter 425 (holotype: MEL2481888 A) .

Pterostylis peakallana ( Fig. 6 , revised key to Vicflora Appendix 7) has affinities to P. exelsa but differs from that species in lacking a crest of small dense setae and a scape 18–58 cm tall (versus up to 80 cm) with 1–8 flowers (versus up to 20). Pterostylis peakallana is similar to P. terminalis but differs in labellum tip not upturned, wider lateral sepals and longer prominent setae. Pterostylis peakallana corresponds to the following illustrations: Backhouse (2019: 357; as P. species ‘north west plains’); Backhouse et al. (2016: 714; as P. ‘north west mallee’ - Yanac photos only).

Deciduous terrestrial, solitary, tuberous herbs. Leaves sessile 2–10 in a rosette, imbricate, green, or withered at anthesis; lamina narrowly elliptical, margins entire, acute to acuminate, 0.5–3.5  0.5–1.0 cm. Scape 18–58 cm tall, 0.2–0.3 cm diam., generally 1–8 flowers, 3.0– 4.5 cm tall, 2.0– 2.5 cm thick. Sterile leafy bracts 4–7, ensheathing stem, lanceolate, acute, withered at flowering, 0.5–3.0 cm long. Floral bracts ovate-lanceolate, not overlapping at base of scape or at apex, clasping stem, apex acute, 2.0–3.5  0.3–1.0 cm. Pedicels erect, glabrous, slender 2–4 cm long, partially enclosed within the floral bract, appressed against the stem. Ovaries erect to slightly porrect, near but not usually against the stem, glabrous, narrowly cylindrical, 4.0–7.0 mm  1.5–2.0 mm. Flowers porrect; galea bulbous, glabrous, gibbous at base, shallowly curved throughout, narrowing to a filiform, apical point; translucent white with predominantly green to light brown stripes and markings; petals mostly translucent white with small light green or brown suffusions, margins incurved with well-developed basal flanges, usually not touching; lateral sepals usually translucent white with light brown or green outline and striping, free points usually light brown-green, basal half of lateral margins covered with prominent white trichomes. Dorsal sepal cucullate, glabrous, broadest nearest the base, 2.0– 2.5 cm long, tapering to an apical filiform, straight to decurved point, 10-14 mm long. Lateral sepals deflexed, narrow at base and conjoined in basal half, flat to shallowly concave lateral margins, sparsely ciliate, conjoined part 8–11 mm long, 7–10 mm wide; free points curved forward, filiform, 11–23 mm long, spreading. Petals asymmetrical obong-lancolate, falcate, 0.8–1.2  4.2–6.2 mm, dorsal margin prominently thickened, glaborus, anterior margin curved, glabrous, proximal flange brown prominent, apex acuminate. Labellum insectiform on a visible claw, articulate, highly sensitive to touch, nested between conjoined part of the lateral sepals when exposed and in set position; 6.2–7.9  1.7–2.9 mm, 0.3–0.4 mm deep, usually solid green or brown, laminar oblanceolate with basal lobe: 1.6–2.5  0.7–1.3 mm, 1.4–2.0 mm wide; distal margins slightly uneven with a series of spreading white setae, largest nearest the base, smaller towards apex, 1.1–2.5 mm long, with twin pairs of prominent long setae, 2.6–4.6 mm long below the basal lobe, occasionally a set of hairs, 1.0– 1.5 mm, extending from the basal mound, not always present. Column porrect, incurved, extending most of the length of the bulbous part of the galea, partly visible through translucent parts of the galea; column wings rectangular, distal margins covered in a series of fine, dense setae. Anther obtuse, green, c. 1 mm long. Pollinia linear, yellow.

Flowering: — Peak flowering November.

Habitat: — Different semi-arid habitats, the first a floristically depauperate, low-lying, seasonally inundated open Eucalyptus woodland on cracking clays dominated by Eucalyptus calycogona subsp. trachybasis and Eucalyptus phenax subsp. phenax , and the second site a diverse open eucalypt woodland dominated by Eucalyptus largiflorens , Bursaria spinosa Cavanilles (1797: 30) , Chrysocephalum semipapposum Steetz in Lehman (1845: 474), Rhodanthe corymbiflora ( Schlechtendal 1848: 448) Wilson (1992: 391) with a diverse understory community of grasses and geophytes.

Distribution: — Currently known from two widely disjunct populations ( Fig. 1 ) within Wyperfeld National Park and a reserve near Boort, with unconfirmed reports from one further location within Wyperfeld National Park.

Conservation status: — Endangered, P. peakallana meets the IUCN criteria ( IUCN, 2012) EN D for endangered with less than 250 individuals known. However, considering the large area of similar habitat within Wyperfeld, Murray Sunset and surrounding reserved areas, adequate surveys for this species in mid-November in years of high rainfall are required to accurately determine its status.

Etymology:— Named in honour of Rod Peakall in recognition of his role in elucidating the pollination mechanisms of many Australian orchids and his contributions to understanding evolution of pollination by sexual deception.

Additional specimens examined:— Australia. Victoria: Wyperfeld National Park, Brocken Bucket , 130 m, 9 Nov 2019, Reiter 426 ( MEL2481889 A) ; Wyperfeld National Park, Brocken Bucket , 130 m, 9 Nov 2019, Reiter 423 ( MEL2481886 A) ; Wyperfeld National Park, Brocken Bucket , 130 m, 9 Nov 2019, Reiter 424 ( MEL2481887 A) ; Marmal NCR, 9 Nov 2019, Reiter 420 ( MEL2481883 A) ; Marmal NCR, 9 Nov 2019, Reiter 422 ( MEL2481885 A) ; Marmal NCR, 104 m, 9 Nov 2019, Reiter 421 ( MEL2481884 A) ; Marmal NCR, 104 m, 3 Nov 2016, Radford s.n. ( MEL2411314 ) ; Marmal NCR, 104 m, 9 Nov 2019, Reiter 433 ( MEL2481896 A) .

Figures

FIGURE 1. Distribution of study sites surveyed: black circles= group 1 (P. biseta); black squares = group 2 (P. jeanesii); white squares = P. jeanesii sites from which there are collected specimens but no plants were found in recent surveys; black triangles = (group 3) P. peakallana.

FIGURE 6. A. Pterostylis peakallana habitat. B. Inflorescence, side view. Photographer: Russell Stanley.