Prostanthera milleri Palsson & J.J.Bruhl, 2025

Prostanthera milleri Palsson & J.J.Bruhl , sp. nov.

( Fig. 12 View Fig , 13 View Fig .)

Type: New South Wales. Central Coast : Olney State Forest , intersection of Walkers Ridge Rd , ~ 5.1 km from junction with Wollombi Forest Rd , Watagan State Forest , 29 Sep. 1987, B. J. Conn 2613 & B. Timmis (holo: NSW 228852 About NSW !; iso: CANB, MEL 2523242 View Materials *, NE 110202 !,? RSA) .

Diagnosis

Prostanthera milleri is morphologically similar to P. dyarubbin and P. faucicola but differs in the strong scent of 1,8-cineole in freshly crushed leaves in P. milleri , absent in P. dyarubbin and P. faucicola ; leaves of P. milleri softer and wider than the leaves of P. dyarubbin (length to width ratio 2.0– 3.4 in P. milleri v. 2.0–5.0 for P. dyarubbin ); anthers of P. milleri cream to mauve v. purple to deep purple in P. dyarubbin .

Shrub, single to multi-stemmed, 1–4 m tall, 1–2 m wide, covered with glandular trichomes (~ 0.1 mm in diameter). Branchlets quadrangular, distinctly 4-ridged, with scattered glandular trichomes and densely distributed antrorse non-glandular hairs in rows on the leaf decurrencies, non-glandular hairs ~ 0.15 mm long, white. Juvenile leaves dentate with up to six small teeth per leaf. Leaves strongly discolourous, mid-green above, paler below; petiole 3– 15 mm long; lamina ovate to lanceolate, 16–47 mm long, 6–16 mm wide, length to width ratio 2.0–3.4, length of maximum width from base to total lamina length ratio 0.2–0.4, base cuneate, sometimes attenuate; margin entire, apex usually obtuse, without non-glandular hairs except for prominent midrib on abaxial surface (sparsely to moderately densely hairy, non-glandular hairs ±antrorse, to 0.15 mm long), in depressed midrib on adaxial surface (depressed for ~2/3 length and with scattered ±antrorse non-glandular hairs to 0.15 mm long) and usually proximal fifth of margin (antrorse simple non-glandular hairs up to 0.15 mm long); abaxial surface moderately to densely glandular (25–45 mm −2); adaxial surface moderately glandular (10–25 mm −2), secondary veins often visible. Inflorescences ±narrow, ±compact thryses to ~ 1.5 cm long with dichasia usually reduced to single flowers. Floral bracts caducous, scutiform and concave, can vary in shape along axis of inflorescence, central floral bracts 1.7–2.6 mm long, 1.7–2.3 mm wide; abaxial surface with scattered non-glandular hairs to 0.15 mm long, scattered to densely distributed glands; adaxial surface without non-glandular hairs, occasional glands; margin ciliate, non-glandular hairs to 0.2 mm long. Pedicel 1.5–2.25 mm long, scattered non-glandular hairs ~ 0.15 mm long, moderately to densely glandular. Floral prophylls persistent, pale green to pale pink, a 1 axis to anthopodium ratio 2–5, opposite, narrowly elliptic, 1.3–2.3 mm long, 0.2–0.4 mm wide, length to width ratio 4–7; abaxially hair- y, scattered glands; margin ciliate to densely ciliate (non-glandular hairs up to 0.2 mm long); adaxially without non-glandular hairs, occasional glands; midrib visible in specimens stored in spirits. Calyx green, green with maroon lobes or all maroon, bilobed, both lobes recurved from corolla; outer surface moderately to densely glandular, scattered non-glandular hairs; margin sparsely to densely ciliate with slightly crisped or adpressed white non-glandular hairs up to 0.1 mm long; inner surface sparsely to densely hairy towards margin of lobes with scattered glandular trichomes, non-glandular hairs up to 0.15 mm long; tube 1.5–2.5 mm long, sometimes ridged in dried specimens; abaxial lobe transversely elliptic to oblate, (1.0–) 1.4–2.3 mm long, 1.6–3.0(–3.8) mm wide at base, apex rounded or occasionally retuse; adaxial lobe transversely elliptic, 0.7–1.7 mm long, 2.0–3.4(–4.1) mm wide at base; apex rounded and margin often shallowly sinuate; adaxial lobe length to abaxial lobe length ratio 0.3–1.2. Corolla blue-purple; adaxial corolla tube length 3.0– 4.5 mm long; outer surface moderately hairy beyond calyx, ±antrorse non-glandular hairs up to 0.1 mm long, sparsely glandular; inner surface tube without non-glandular hairs, sparsely glandular, abaxial lobe usually without non-glandular hairs, adaxial lobe hairy to densely hairy, non-glandular hairs to 0.1 mm long, lateral lobes ±without non-glandular hairs to hairy, non-glandular hairs to 0.1 mm long; corolla margin densely to very densely ciliate with crinkled white non-glandular hairs, 0.04–0.15 mm long; abaxial median lobe oblate to elliptic, 1.5–3.0 mm long, 1.6–3.0 mm wide, 1.0– 2.2 mm wide below distal lobing, length to width ratio 0.7–1.5, apex rounded and margin regular in fresh specimens; lateral lobes usually shallowly triangular to deltate, sometimes oblate, 1.4–3.0 mm long, 1.5–3.4 mm wide, length to width ratio 0.7–1.1, apex rounded, margin regular in fresh specimens; adaxial median lobe-pair depressed ovate, 0.6–1.3 mm long, 1.4–3.0 mm wide, length to width ratio 0.3–0.7, apex rounded, margin regular in fresh specimens. Stamens abaxial stamens inserted 0.6–1.5 mm above corolla base, filaments 1.0–2.5(–4.2) mm long; adaxial stamens inserted 0.5–1.1 mm above corolla base; filaments 0.9– 2.3 mm long; anther locules 0.7–1.3 mm long; anthers cream to mauve, connective extended to form 1 or 2 basal appendages (one appendage usually shorter than the other), extending beyond base of anther and terminating with 6–12 translucent mauve conical hairs, length beyond the anther of appendage including hairs to ~ 0.2 mm, hairs to 0.1 mm. Pistil 4–7.5 mm long; ovary cylindrical obovoid, 0.6–0.7 mm long, diameter at base ~ 0.5 mm, lobes ~ 0.3 mm long; style 3.5–5(–6.8) mm long; stigmatic lobes 0.2–0.4 mm long. Fruiting calyx accrescent. Mericarps, mature colour unknown, to ~ 1.8 mm long, wrinkled and minutely papillose.

Phytochemistry

Although P. milleri contains large quantities of the essential oil 1,8-cineole and some p-cymene, this species also contains E-verbenol and menth-3-en-8-ol that are essential oils not found in P. ovalifolia sens. lat., P. cineolifera or P. dyarubbin (tables 2, 4 in Sadgrove et al. 2020; Supplementary Table S4) and the latter chemical gives the crushed leaves a distinctive sent.

Distribution

Prostanthera milleri occurs in Olney State Forest, Watagan Mountains in the Wyong subregion of the Sydney Basin bioregion ( Fig. 6 View Fig ).

Habitat

This species grows on ridges and slopes at altitudes of ~ 450 m. This site is on Hawkesbury Sandstone but downslope of a small basalt remnant ( Colquhoun et al. 2022). The vegetation is recorded as eucalypt shrubby open forest–shrubby tall open forest with dominant species Eucalyptus piperita , Corymbia eximia and Syncarpia glomulifera , and an E. agglomerata plantation. Associated species include Allocasuarina torulosa , Acacia elata , Astrotricha latifolia , Zieria smithii , Smilax australis and Calochlaena dubia .

Phenology

Flowers have been recorded from late September–October with fruit recorded in November.

Conservation status

There is only one known population of P. milleri , with>1000 plants recorded in 2017, in an AOO <10 km 2. In 2022, this population had decreased by at least 70%, likely as a result of the severe drought that ended in early 2020. The population is ±a single age cohort with some recruitment close to the road where the leaf litter is relatively shallow. Downslope where there is leaf litter up to 20 cm deep, no recruitment was noted in 2022. Based on the AOO and severe decline in the number of mature individuals, we suggest a ‘Critically Endangered’ status is appropriate under the International Union for Conservation of Nature (2019), fulfilling Criteria B2 (a) and (b)(iv). The known population occurs within a section of state forest marked as ‘forest management zone 2- a permanent exclusion to harvesting’ (Mark Drury, Forestry Corporation of NSW, pers. comm., 2022). Nearby ridges in Olney State Forest have been searched unsuccessfully for further populations of P. milleri .

Etymology

Honouring Robert T. Miller, who informally documented and provided extensive descriptions for the ‘Hawkesbury River’ and ‘Wattagan State Forest’ variants of P. ovalifolia ( Miller 1988) . Miller was a very active member of the ‘ Prostanthera and Westringia Study Group’ of the Society for Growing Native Plants from the early 1980s, becoming leader of the study group from 1992 until closure in 2006.

Notes

The closest known population of P. dyarubbin to the known population of P. milleri is the Mogo Creek population, 25 km to the south-west. We have propagated cuttings of P. milleri and distributed plants to the Australian National Botanic Gardens.

Selected specimens examined

NEW SOUTH WALES: Central Coast. Olney State Forest, intersection of Walkers Ridge Rd and Murrays Forest Rd, 11 Oct. 2017, R. L . Palsson 166, R. L . Andrew, J. J . Bruhl & I. R . Telford ( AD!, BRI!, CANB!, K!, M!, MEL!, MO!, NE!, NSW!, US!); Olney State Forest, intersection of Walkers Ridge Rd and Murrays Forest Rd, 11 Oct. 2017, R. L . Palsson 161, R. L . Andrew, J. J . Bruhl & I. R . Telford ( NE!); Olney State Forest, intersection of Walkers Ridge Rd and Murrays Forest Rd, 18 Nov. 2017, R. L . Palsson 215 & M. R . Donald ( CANB!, MEL!, NE!, NSW!) .