Maesa prolatifructa Sumanon & Utteridge, 2021

Sumanon, Pirada, Eiserhardt, Wolf L., Balslev, Henrik & Utteridge, Timothy M. A., 2021, Six new species of Maesa (Primulaceae) from Papua New Guinea, Phytotaxa 505 (3), pp. 245-261 : 256-259

Maesa prolatifructa Sumanon & Utteridge , sp. nov. ( Fig. 6 )

Recognised in the genus Maesa by the combination of the following characters: comparatively long petioles up to 4 cm long, lanceolate leaves with a coriaceous lamina, and the leaves drying olive-green with a reddish brown abaxial midrib.

Type:— PAPUA NEW GUINEA. East New Britain District: Pomio Subdistrict, lower slopes of Mt Lululua , 5°43’S, 151°2’E, elev. 1250 m, 6 May 1973 (fr.), P. F . Stevens & Y . Lelean LAE 58298 (holotype K!; isotypes BISH!, CANB!, L image!, M!) .

Tree or shrub to 18 m. Indumentum: all parts lacking hairs, scaly on lamina surfaces; scales peltate, up to 0.9 mm in diameter, reddish brown or ginger brown with a central dark spot, ± sessile, circular. Branches drying dark reddish brown with scattered lenticels, glabrous. Leaves: lamina lanceolate, 7.3–11.7 cm long, 2.4–4.2 cm wide, coriaceous, adaxial surface glabrous, abaxial surface scaly, base attenuate or cuneate, margins entire and distinctly marginate on drying (i.e. with the marginal tissue raised and distinct), apex acute; midrib glabrous, distinctly raised abaxially, drying olive-green adaxially and reddish brown abaxially, secondary veins 5–8 pairs, craspedodromous; petiole 1.8–4.0 cm long, glabrous. Staminate inflorescences and flowers not seen. Pistillate inflorescences lateral (axillary), racemes, solitary or fasciculate with up to 3 inflorescences per axil, 2–3 cm long at anthesis, 3–7 cm long in fruit, axis densely scaly; pedicels 1.2–1.7 mm long, densely scaly distally; bracts triangular, 1.2–1.5 mm long, scaly, margins entire to ciliate, apex acute; bracteoles ±opposite, inserted at the base of the hypanthium, shape as bracts, 0.9–1.2 mm long, 0.75–0.90 mm wide. Pistillate flowers pentamerous; calyx lobes ovate, 0.75 mm long, 0.75–0.85 mm wide, glabrous, margins entire, apex acute; corolla not seen; hypanthium 1.5–2 mm long, scaly to sparsely scaly; style not seen. Fruits ellipsoid, prolate at the poles, reddish brown, 6.0–10.0 mm long, 4.0– 5.7 mm diameter, scaly; pedicels in fruit 3.0–6.0 mm long; bracteoles remaining ±opposite each other at the base of the fruit; calyx lobes overlapping, persistent.

Distribution and ecology:— The species is found at an elevation of 1250–1500 m in montane forests of New Ireland and New Britain in Papua New Guinea.

Etymology:— The specific epithet refers to the prolate, ellipsoid fruit of this new species, a feature found in this taxon and in M. sayersii Sleumer.

Additional material examined:— PAPUA NEW GUINEA. East New Britain District: Pomio Subdistrict, Mt Sule , about 25 miles NNE of Fulleborn Harbour, 5°50’S, 150°50’E, elev. 1500 m, 7 May 1973 (fr.), J. R. Croft & P. Katik NGF 41940 (distributed partly as 14940) ( BISH!, CANB!, E!, K!, L image!) ; New Ireland Province: Namatanai Sub-province, Hans Meyer Range, on steep ridge near camp, c. 8 km W. N. W. of Taron on east coast, 4°24’S, 152°58’E, elev. 1350 m, 23 October 1975 (fl. & fr.), M. J. S. Sands 2329 ( K!, L image!) .

Notes:— Maesa prolatifructa is unique in the genus in having lanceolate leaves with a reddish-brown raised midrib on the abaxial side. It is unlikely to be confused with any other species in New Guinea and can be easily distinguished from its most similar species, M. sayersii , by leaf characters, viz: coriaceous texture (chartaceous to sub-coriaceous in M. sayersii ), shape (lanceolate vs elliptic in M. sayersii ), length and width ratio (2.1–4.3 vs 1.7–3.2 in M. sayersii ), size (7.3–11.7 cm long by 2.4–4.2 cm wide vs 11.5–28.8 cm long by 4.0– 15.5 cm wide in M. sayersii , Fig. 7 ), and venation (5–8 secondary vein pairs per leaf vs 6–10 in M. sayersii ). The distribution of M. prolatifructa , as currently known, is limited to East New Britain and New Ireland Provinces of Papua New Guinea, while M. sayersii is distributed in West New Britain, New Hanover, New Ireland and Manus Island. Maesa prolatifructa is also found at higher elevations around 1250–1500 m, while M. sayersii is at lower elevations around 30– 900 m.

Several previous studies have pointed out the effect of elevation gradients on morphological and anatomical variation within species. Most studies showed a decrease in leaf size and an increase in leaf thickness of plants growing at high elevations as a modification to the environment (e.g., Scheepens et al. 2010, Bresson et al. 2011), posing the question: is this new species an altitudinal variant of M. sayersii? To test this, a correlation test was performed to see if there is any correlation between elevation and leaf length or leaf width. Although the sample size was small, there is no significant correlation between elevation and leaf size in both species, and mean length and width of both species are significantly different ( Fig. 7 and Table 1); this evidence further supports recognition of M.prolatifructa as a distinct species. Further studies using population genetic methods could clarify and confirm the taxonomic status of these two species.

Figures

FIGURE 6. Maesa prolatifructa Sumanon & Utteridge. A habit; B node with petiole and base of inflorescence; C abaxial surface of leaf; D terminal portion of inflorescence; E hydrated flowers, one large calyx lobe removed, young ‘dome’ of corolla visible; F flower to show young corolla ‘dome’; G corolla from below showing insertion point of young stamen (5-merous flower); H corolla opened flat; I fruit, dry; J fruit after soaking; K detail of scales from fruit surface. A, C, I–K from Stevens & Lelean. LAE 58298 (K); B, Croft & Katik NGF 41940 (K); D–H Sands 2329 (K). Scale bars: single bar = 1 mm, graduated single bar = 5 mm, double bar = 1 cm, graduated double bar = 5 cm. Illustration by Andrew Brown.

FIGURE 7. Leaf comparison between M.sayersii and M.prolatifructa. A Leaves of M. sayersii; B Leaves of M. prolatifructa; C a boxplot showing leaf length of each species; D a boxplot showing leaf width of each species. Scale bar = 5 cm. Illustration by Pirada Sumanon.