Prostanthera dyarubbin Palsson & R.T.Mill., 2025

Prostanthera dyarubbin Palsson & R.T.Mill. , sp. nov.

( Fig. 8 View Fig , 9 View Fig .)

Type: New South Wales. Central Coast: Bicentenary Rd , 3.2 km SW of Wisemans Ferry, 1 Sep. 2017, R. L . Palsson 100 & M. R . Donald (holo: NSW!; iso: AD!, BRI!, CANB!, K!, MEL!, MO!, NE 106387 !) .

Prostanthera sp. 10 (Hawkesbury, B. J.Conn 2591), J.D.Briggs & J. H.Leigh, Rare or Threatened Austral. Pl. 81 (1996).

Prostanthera sp. Hawkesbury ( B. J.Conn 2591) NSW Herbarium, CHAH, Australian Plant Census, https://id.biodiversity.org.au/tree/51689388/ 51241805 [accessed 10 Oct 2024].

Prostanthera dyarubbin is characterised by persistent floral prophylls 1.6–3.6 mm long, with non-glandular hairs, recurved calyx lobes, a compact inflorescence and no scent of 1,8-cineole when crushed, and differs from P. cineolifera and P. ovalifolia in the loose open inflorescence, adpressed calyx lobes, caducous floral prophylls and strong 1,8-cineole scent of these species.

Shrub single- to multi-stemmed to (1–) 4–6 m tall, up to 2 m wide. Branchlets quadrangular, distinctly 4-ridged, covered with scattered glandular trichomes ~ 0.1 mm in diameter and densely covered with antrorse non-glandular hairs in rows on the leaf decurrencies, non-glandular hairs 0.15–0.3 mm long, white. Juvenile leaves larger than adult leaves, margins often dentate with up to six small teeth per leaf, some populations retain few to many dentate leaves on mature plants. Leaves dark green above, sometimes tinged with purple, paler below; petiole 2–10 mm long; lamina lanceolate, 8–30 mm long, 4–12 mm wide, length to width ratio 2.0–5.0, length of maximum width from base to total lamina length ratio 0.3–0.4, base attenuate to cuneate, margin entire, apex obtuse, non-glandular hairs absent except for prominent midrib on abaxial surface (non-glandular hairs distributed densely, ±antrorse, 0.05–0.2 mm long) and usually proximal third of margin (antrorse simple non-glandular hairs up to 0.2 mm long); abaxial surface moderately to densely glandular (15–30 mm −2); adaxial surface sparsely glandular (1–10 mm −2), secondary veins indistinct. Inflorescences ±narrow, compact thryses to ~ 6 cm long with dichasia usually reduced to single flowers. Floral bracts caducous, ±obtrullate and concave, vary in shape along axis of inflorescence, central floral bracts 2.5–5.0 mm long, 2.0– 3.5 mm wide; abaxially scattered ±antrorse non-glandular hairs 0.05–0.2 mm long, sparsely to densely glandular; adaxially non-glandular hairs absent, occasional glands; margins ciliate with non-glandular hairs to 0.2 mm long. Pedicel 0.5–2.7 mm long, scattered non-glandular hairs ~ 0.1 mm long, moderately glandular. Floral prophylls persistent pink to maroon, a 1 axis to anthopodium ratio 3–4 (in some populations floral prophylls inserted immediately below calyx), opposite, narrowly elliptic, 1.6–3.6 mm long, 0.2–0.6 mm wide; margin and abaxial surface moderately to densely covered by non-glandular hairs to 0.3 mm long; adaxial surface with non-glandular trichomes absent, with scattered glands. Calyx usually maroon, bilobed, both lobes recurved; outer surface hairy mainly on the tube (non-glandular hairs to 0.1 mm), densely glandular; inner surface proximally without non-glandular hairs, lobes variable from ±without non-glandular hairs to densely hairy towards margin of lobes; margin sparsely to densely ciliate, with white non-glandular hairs up to 0.1 mm long; tube 1.5–2.5 mm long; abaxial lobe broadly ovate, 1.0– 4.0 mm long, 1.5–4.0 mm wide; adaxial lobe broadly depressed ovate, 0.7–2.3 mm long, 2.0– 4.5 mm wide; apex usually rounded; fruiting calyx somewhat enlarged in fruit. Corolla mauve–purple; adaxial corolla tube length 3.5–5 mm long; outer surface sparsely to moderately hairy, antrorse non-glandular hairs up to 0.2 mm long, scattered glands; margin usually densely ciliate, non-glandular hairs up to 0.1 mm long; inner surface usually with scattered antrorse non-glandular hairs up to 0.15 mm, particularly on the lobes, scattered glands; abaxial median lobe broadly oblong to ovate, 1.4– 3.3 mm long, 1.4–3.5 mm wide at widest; lateral lobes ovate, 1.7–3.3 mm long, 1.2–3.5 mm wide, apex rounded to ±acute; adaxial median lobe -pair broadly ovate, each lobe 1.2–2.75 mm long, 0.75–1.5 mm wide. Stamens with filaments 0.8–1.3 mm long; anthers purple to deep purple; locules 0.75–1.0 mm long; connective extended to form 1 or 2 basal appendages (one appendage usually shorter than the other), extending beyond base of anther and terminating with 15–35 translucent purple conical hairs; length beyond the anther of appendage including hairs 0.1–0.3 mm; hairs to 0.1 mm. Pistil 4.5–6 mm long; ovary cylindrical obovoid, 0.8–1.0 mm long, diameter at base 0.6–0.8 mm, lobes 0.4–0.5 mm long; style 3.5–4.5 mm long; stigmatic lobes to 0.5 mm long. Mericarps maturing to dark brown, ~ 1.5 mm long, wrinkled and minutely papillose, distally ~ 0.8 mm extended beyond base of style.

Phytochemistry

Although P. dyarubbin contains small quantities of 1,8-cineole and prostantherol, this species also contains four oils not found in P. ovalifolia sens. lat., P. cineolifera or P. milleri , namely, cadilene, 1-hexanol, 2-hexanol and (E)-2-hexenal (tables 2, 4 in Sadgrove et al. 2020; Supplementary Table S4).

Distribution

Known populations of P. dyarubbin are in the Pittwater and Yengo subregions of the Sydney Basin bioregion, in the environs of the lower Hawkesbury River from Mogo Creek southwards to near Hornsby and from near Webbs Creek eastwards to Ku-ring-gai Chase National Park ( Fig. 6 View Fig ).

Habitat

The species grows on dry ridges, rocky slopes, along cliff lines and in gullies at altitudes up to 150 m on sandstones of the Narrabeen Group and Hawkesbury Sandstone ( Colquhoun et al. 2022). The vegetation is eucalypt shrubby open forest with Eucalyptus punctata , Angophora bakeri , A. costata and Corymbia eximia recorded as dominants. Associated species include Allocasuarina littoralis , Astrotricha longifolia , Grevillea buxifolia , G. sericea and Actinotus helianthi .

Phenology

Flowers are recorded from August–October with fruit from early October.

Conservation status

The species is conserved in Dharug National Park, Ku-ring-gai Chase National Park, Parr State Conservation Area, Popran National Park, Wisemans Ferry Historic Site and Yengo National Park. There are undoubtedly many more populations of P. dyarubbin that remain undiscovered within the relatively unexplored areas of the distribution. We recommend a status of ‘Least Concern’ (International Union for Conservation of Nature 2019).

Etymology

The species epithet is the traditional Dharug (Darug/Daruk) name for the Lower Hawkesbury area. There are several Indigenous spellings for the name of the river (Dyarubbin, Dyarrubin, Deerubbin, Deerubbun). We have selected Dyarubbin, the most commonly used spelling that is also used by the Darug Custodian Aboriginal Corporation (see https://www.dyarubbin.com/).

Notes

Prostanthera dyarubbin is morphologically similar to P. milleri Palsson & J.J.Bruhl and P. faucicola Palsson & I.Telford , sharing relatively large persistent hairy floral prophylls, recurved calyx lobes and a compact inflorescence. The known distribution of P. dyarubbin is remote from the known distribution of P. faucicola in the Macleay Gorges ( Fig. 6 View Fig ). Prostanthera dyarubbin differs from P. milleri in the lack of the scent of 1,8-cineole in freshly crushed leaves of the former. The short anther appendages of P. dyarubbin have 15–35 conical hairs v. 6–12 in P. milleri . The leaves of P. dyarubbin tend to be tougher and narrower that the leaves of P. milleri (length to width ratio 2.0–5.0 for P. dyarubbin v. 2.0– 3.4 in P. milleri ). The anthers of P. dyarubbin are purple to deep purple v. mauve for P. milleri .

A horticultural selection of the species was brought into cultivation by Henry Parry, Floralands Nursery, Maghoney Creek, New South Wales, under the name Prostanthera ‘Violet Beauty’. The selection ‘differs from the typical form in the intensity of the leaf and calyx colouration that is deeper than the normal colour range during flowering’ ( Miller 1988).

Selected specimens examined

NEW SOUTH WALES: Central Coast: Eastern Dyarrubin , 12 June 1996, A . Bofeldt s.n. ( NSW 888576 About NSW !); Wisemans Ferry , ~ 15 km N towards St. Albans , 4 Oct. 1984, T. A . James 568 ( NSW!); Wisemans Ferry , 0.1 km S on Old Northern Road , 22 Sep. 1987, B. J . Conn 2591 ( NSW!); Kuring-gai Chase, Coal and Candle Creek Road, 12 Oct 1964, O . D. Evans s.n. ( NSW 71554 About NSW !); Bar Point, ~ 3 km along Pacific Motorway from N end of Hawkesbury River bridge, 5 Oct. 2017, R. L . Palsson 133 & M. R . Donald ( NE!, NSW!); Hawkesbury River , Oct. 1916, H. M. R . Rupp s.n. ( NSW 228302 About NSW !); Brisbane Water National Park, Mullet Creek , Nov. 1890 L . Stephenson s.n. ( NSW 134072 About NSW !) .