Prostanthera volucris R.P.O’Donnell, 2023

O’Donnell, Ryan P., Bruhl, Jeremy J., Telford, Ian R. H., Wilson, Trevor C., Zimmer, Heidi C., Taseski, Guy M. & Andrew, Rose L., 2023, Molecular and morphological analyses support recognition of Prostanthera volucris (Lamiaceae), a new species from the Central Tablelands of New South Wales, Australian Systematic Botany 36 (1), pp. 1-20 : 12-17

Prostanthera volucris R.P.O’Donnell , sp. nov. ( Fig. 7 , 8 )

Type: Australia: New South Wales: Central Tablelands: Evans Crown Nature Reserve , ~ 2.8 km SE of Tarana township, 28 Oct. 2018, G. M. Taseski 853, (holo: NSW 1055966 (sheet) and NSW 1057497 (spirit; listed as an associated collection on NSW 1055966); iso: BRI, CANB, K, MEL, MO, NE 110628, P, UNSW). Prostanthera sp. Evans Crown ( G. M.Taseski NSW 1055966) ( O’Donnell et al. 2021 a).

Diagnosis

Prostanthera volucris can be distinguished from the morphologically similar P. gilesii by its larger prophylls, 3.8–9 mm long, 0.8–4.5 mm wide (v. <4 mm long, <0.6 mm wide for P. gilesii ), densely hairy branches, calyces and prophylls (up to 80 v. up to 40 trichomes mm− 2 for P. gilesii ), appressed to subappressed retrorse trichomes ( v. antrorse for P. gilesii ) and densely hairy abaxial and adaxial lamina surfaces ( v. predominantly glabrous with occasional antrorse trichomes restricted to the abaxial surface midrib for P. gilesii ). Prostanthera volucris can also be distinguished from P. phylicifolia and P. gilesii by its mericarps that are rugose and papillose, with occasional long pilose trichomes ( v. reticulate , not distinctly papillose and glabrous for P. phylicifolia; mature mericarps have never been observed for P. gilesii ; Table 4 ).

Compact, erect shrub up to 80 cm high, with plants forming tight mats. Branches ± terete, occasionally quadrangular early in development, becoming terete with age, densely hairy (20–80 trichomes mm −2); trichomes 0.1–0.4 mm long, appressed to subappressed, retrorse, straight to slightly curled, white; sessile glands indistinct or absent (obscured by indumentum). Leaves velutinous, appearing silver–light green, slightly paler on abaxial surface, occasionally becoming red after prolonged exposure to strong sunlight, not aromatic when touched or crushed; petiole 0.88–1.4 mm long, densely hairy (20–48 trichomes mm −2), the trichomes 0.2–0.8 mm long, appressed to subappressed, retrorse, straight to slightly curled, white; lamina narrowly ovate to elliptic, 12–19 mm long, 3–5 mm wide, with length to width ratio 2.6–5.3 and length of maximum width from base to total lamina length ratio 0.1–0.4; abaxial surface moderately to densely hairy, particularly on midrib (16–40 trichomes mm −2), the trichomes 0.2–0.4 mm long, spreading to erect (occasionally retrorse along midrib), straight to slightly curled, white; abaxial lamina glands indistinct; adaxial surface moderately to densely hairy (16–30 trichomes mm −2), the trichomes 0.1–0.3 mm long, spreading to erect, straight to slightly curled, white; adaxial lamina glands indistinct; base obtuse (occasionally appearing attenuate because margin more involute towards base); margin recurved; apex obtuse; venation indistinct, the midrib slightly raised on the abaxial surface. Inflorescence a frondose botryoidal conflorescence of monadic uniflorescences with 4–8-flowers per conflorescence. Podium a 1 axis 0.9–2.8 mm long, densely hairy (30–60[–88] trichomes mm −2), the trichomes 0.1–0.2 mm long, appressed to subappressed, retrorse, straight to slightly curled, white, with glands indistinct or absent (obscured by indumentum); anthopodium absent or indistinct. Pherophylls not seen. Prophylls ± persistent, inserted near base of calyx, opposite, narrow-ovate to narrowly elliptic, 3.8–9 mm long, 0.8–4.5 mm wide, the length to width ratio 1.8–5.6, the length of maximum width from base to total lamina length ratio 0.3–0.9, densely hairy (16–56 trichomes mm −2), the trichomes 0.1–0.2 mm long, appressed to subappressed, retrorse, straight to slightly curled, white, with glands indistinct or absent (obscured by indumentum); base slightly attenuate; margin entire; apex obtuse; venation indistinct. Calyx tube 1.5–2.1 mm long, light green, occasionally darkening to dark mauve with sun exposure; abaxial lobe ovate to broadly ovate, 2–4 mm long, 2–4 mm wide at base, the apex rounded to retuse; adaxial lobe ovate to elliptic, 3–5.3 mm long, 2.1–4.2 mm wide at base, the length to width ratio 1.2–1.4, the apex ± rounded; the adaxial lobe length to abaxial lobe length ratio ~1.3; outer surface densely hairy (24–64 trichomes mm −2), the trichomes 0.2–0.35 mm long, appressed to subappressed, retrorse, straight to slightly curled, white, with glands indistinct or absent (obscured by indumentum); inner surface of tube glabrous; inner surface of lobes moderately to densely hairy near margin and apex, the trichomes appressed to subappressed, spreading to occasionally antrorse, straight to slightly curled, white. Corolla 14–18 mm long, white, with purple to dark mauve speckled markings on the inner surface of the tube and pale orange to yellow markings on base of abaxial median lobe; tube 3–5 mm long; abaxial median lobe broadly spathulate, 7–9.5 mm long, 4–7 mm wide (below distal lobing), length to width ratio 1.4–1.8, the apex slightly irregular and rounded, bilobed (sinus 2–2.3 mm long, 2.5–3 mm wide distally); lateral lobes oblong to slightly elliptic, 5.4–5.7 mm long, 3.1–3.8 mm wide, length to width ratio 1.5–1.8, the apex rounded, slightly irregular; adaxial median lobe-pair broad to depressed-ovate, 6–7 mm long, 9–9.5 mm wide, length to width ratio 0.6–0.8, the apex rounded, irregular, bilobed (sinus 0.6–0.8 mm long, 0.9–1.6 mm wide, the median margin of lobes occasionally overlapping slightly); outer surface sparsely glandular, moderately hairy, particularly on lobes (8–24 trichomes mm −2), the trichomes 0.1–0.4 mm long, erect to spreading along tube before becoming appressed to subappressed and antrorse on lobes; inner surface ± glabrous, the lobes sparsely hairy to moderately hairy at the tube opening rim and sinuses between lobes, the trichomes 0.1–0.2 mm long, crinkled. Stamens inserted 2.8–4.1 mm above base of corolla; filaments 3.1–5.4 mm long, white, often with mauve tinge; anthers 1.4–1.8 mm long, minutely papillose with an acumen at the base of each lobe and trichomes between lobes, the trichomes 0.1–0.2 mm long, white; connective appendage 0.8–1.5 mm long, dark mauve maturing to yellowish-brown, with a few narrowly triangular trichomes that are 0.1–0.35 mm long and white. Disc 0.5–1 mm long. Pistil 7.5–9.5 mm long; ovary cylindrical-obovoid, 0.9–1 mm long, at base 0.9–1 mm diameter, the lobes 0.5–0.65 mm long; style 7.5–8 mm long; stigma lobes 0.3–0.4 mm long. Fruiting calyx not strongly accrescent, the abaxial lobe clasping to conceal developing mericarps, the adaxial lobe not strongly reflexed. Mature mericarps 1.8–2.1 mm long, 1–1.2 mm wide, rugose, minutely papillose, with a few spreading trichomes that are 0.2–0.5 mm long and white.

Distribution

Known from a single granitic tor in the Evans Crown Nature Reserve , south-east of Tarana , New South Wales, Australia ( Fig. 1 ). This location is situated within the Central Tablelands Botanical Division and South Eastern Highlands IBRA Region ( NSW National Parks and Wildlife Service 2009) .

Habitat

Prostanthera volucris grows on exposed granite formations at 1000–1020 m altitude, along drainage crevices in shallow, skeletal humic soils, with Cyphanthera albicans and Cheilanthes sieberi nearby.

Etymology

From the Latin ‘ volucris ’ (‘winged’ or ‘winged creature’), in reference to the substantial and densely hairy prophylls, which, inserted at the base of the calyx, give the calyx the appearance of being winged.

Ecology and conservation

Although the first collector of P. volucris described it as ‘locally abundant in rock crevices’ (McKee 7043, NSW 237164), only one population is known. More intensive surveys of the Evans Crown Nature Reserve and other unexplored vegetation islands in the nearby area should be undertaken. Because P. volucris is known to grow only on exposed, granitic outcrops, future attempts to locate additional populations should prioritise these landscape features.

The pollinators of P. volucris are unknown; however, its floral characteristics correspond with a floral type visited primarily by bees, although not excluding other insects such as flies ( Wilson et al. 2017). Studies of foraging ranges in Australian bees found a typical maximum foraging range of ~ 700 m ( Smith et al. 2017), which suggests that pollen is unlikely to travel further than this distance. Because P. volucris grows in tight, tangled mats, it is difficult to determine the limits of individual plants. Pairwise shared allele frequencies indicate that some samples represent ramets from a clonal parent, whereas others represent separate individuals. Seedlings have been observed in recent surveys and mature individuals have been observed to set seed; however, it is unknown what proportion of seed set is viable. Because P. volucris is known to occur along drainage crevices, it is likely that seeds are being dispersed primarily by water runoff.

It is unknown whether P. volucris is subject to herbivory; however, as other species of Prostanthera have been observed to be grazed by herbivores, similar threats may apply in this instance ( Jusaitis 2018). Sheep and goats have been known to access the reserve from neighbouring properties and there are currently no feral animal control programs implemented for the reserve ( NSW National Parks and Wildlife Service 2009). The reserve is a popular attraction for hikers and rock climbers, and because the species occurs on a geologically striking outcrop, human activity is a likely threat to this population. On revisiting the site following the severe drought conditions of 2019 –2020, the population appeared to be severely affected by heat and drought stress and had declined substantially in condition ( G. M. Taseski, pers. obs., 2020). Projected prolonged drought conditions and heightened temperatures may adversely affect this population, particularly on account of its highly exposed habitat.

Given the horticultural potential of P. volucris , this species could be a target of increased collecting pressure. Attempts are underway to develop an ex situ collection with botanic gardens and native plant wholesalers. The known distribution of this species is restricted such that the area of occupancy and extent of occurrence are not greater than 4 km 2. Because this species is known from only one highly restricted population of <250 mature individuals where decline in response to drought stress has been observed, we suggest that this species satisfies the criteria to be considered Critically Endangered under the New South Wales Biodiversity Conservation Act 2016 (see https:// www.legislation.nsw.gov.au/view/html/inforce/current/ act-2016-063#statusinformation), the Environment Protection and Biodiversity Conservation Act 1999 and the IUCN Red List criteria thresholds (International Union for Conservation of Nature and Natural Resources 2022).

Notes

Although quantifiable mericarp characters were not included for morphological analyses, differences in mericarp morphology were observed between P. volucris and P. phylicifolia . The mericarp is rugose and distinctly papillate in P. volucris , whereas it is reticulate and not distinctly papillose in P. phylicifolia . Scant attention has been paid to mericarp surface ornamentation and sculpting in recent descriptions of Prostanthera , with the exception of Williams et al. (2006) in their treatment of the P. spinosa complex and Guerin’s (2005) study of mericarp morphology in the Westringieae. The findings outlined here and by Guerin (2005) and Williams et al. (2006) highlight that mericarp morphology may be taxonomically informative in Prostanthera . Further examination of mericarp morphology across the genus is warranted and may provide additional characters for distinguishing among closely related species in future diagnoses.

Other specimens examined

AUSTRALIA: NEW SOUTH WALES: CENTRAL TABLELANDS : South Eastern Highlands: Evans Crown Nature Reserve : H.S. McKee 7043, 10 Jan. 1960 ( NSW237164 ); A.N. Rodd 11009, 9 Mar. 2002 ( NSW856887 ); R.P. O’Donnell & G.M. Taseski 28, 7 Apr. 2020 ( NSW1100357 ); R.P. O’Donnell & G.M. Taseski 29, 7 Apr. 2020 ( NSW1100369 ); R.P. O’Donnell & G.M. Taseski 30, 7 Apr. 2020 ( NSW1100379 ); R.P. O’Donnell & T.C. Wilson 55, 4 Oct. 2020 ( NSW1100402 ); R.P. O’Donnell & T.C. Wilson 56, 4 Oct. 2020 ( NSW1100403 ).

Figures

Fig. 7. (Caption on next page)

Fig. 8. Photograph images of Prostanthera volucris. (a) Habitat and associated vegetation; (b) habit; (c) habit, close-up; (d) flower and bud. Images: R. P. O’Donnell.

Fig. 1. Occurrence records of Prostanthera gilesii, P. phylicifolia sens. str. and the Evans Crown population obtained from Australia’s Virtual Herbarium (2021) after removal of misidentified records and accessions of P. phylicifolia s. lat. as identified by O’Donnell et al. (2021). Populations sampled in this study for genomic analysis (Supplementary Table S1) are indicated with larger, transparent circles, and populations with associated herbarium vouchers that were measured for morphological phenetic analysis (Supplementary Table S2) are indicated with crosses.