Diplycosia platyphylla (Ericaceae), a new species from Mindanao, Philippines

Abstract Diplycosia platyphylla P.W.Fritsch, a new species from Mindanao Island, Philippines, is described and illustrated. This species is most similar to the Bornean Diplycosia urceolata but differs by its green or slightly flushed pink petioles 4–7 mm long, wider leaf blades, acute calyx lobe apices, and lavender mature fruiting calyx. The new species is known only from a single collection made from Mount Apo in North Cotabato Province, southern Mindanao.


Introduction
Diplycosia Blume (Ericaceae: Vaccinioideae: Gaultherieae) comprises about 116 species distributed throughout Southeast Asia and New Guinea (Sleumer 1967;Argent 1982Argent , 1989Argent , 2002Ferreras and Argent 2011;Argent 2013Argent , 2014Fritsch and Amoroso in press;Fritsch and Bush in press). Th e genus can be delimited from other genera of the tribe by a base chromosome number of x = 18 (vs 11), and a combination of (usually) entire leaf margins, fasciculate infl orescences, paired bracteoles borne at the apex of the pedicel, anthers with terminal tubules but with neither spurs nor disintegration tissue, and a capsule surrounded by an accrescent, fl eshy calyx, or rarely a berry. Molecular studies strongly support the monophyly of the genus, and place it as phylogenetically nested within Gaultheria Kalm ex L. in the Wintergreen Group clade (Powell and Kron 2001;Bush et al. 2009;Fritsch et al. 2011).
Nine species of Diplycosia are currently recognized in the Philippines, three having been described since the taxonomic treatment of Ericaceae for the Flora Malesiana (Sleumer1967; Ferreras and Argent 2011;Argent 2013;Fritsch and Amoroso in press). Because species of Diplycosia are often restricted to a single mountain or very few locations, more Philippine species of this genus likely await discovery (Argent 2013). Five species of Diplycosia have been documented from the island of Mindanao (Pelser et al. 2011 onwards;Fritsch and Amoroso in press), the southernmost major island of the Philippines. In April-May 2014 a joint botanical expedition was undertaken by the California Academy of Sciences and the CEBREM Offi ce of Central Mindanao University to mountain peaks in the central part of Mindanao. Several individuals of Diplycosia were observed on Mt. Apo, the highest peak in the Philippines at 2954 m a.s.l. Th ese plants appeared not to match any other Philippine species of the genus, according to the key in Argent (2013). Further study of a collection and photographic images made from these plants confi rmed that these individuals represent a species new to science, which is here described and illustrated.
Etymology. Th e species is named for its notably wide leaves relative to those of most other species in the genus.
Phenology. Flowering and fruiting in April. Distribution and habitat. Diplycosia platyphylla is known only from a single location on Mt. Apo, Mindanao Island, North Cotabato Province, Philippines. Several Conservation status. Diplycosia platyphylla is known from a single population and single collection, with only several plants seen. Although the species is aff orded pro-tection by its occurrence in Mount Apo National Park, it is at risk through apparent extreme rarity. We categorize this species as Critically Endangered (CR): D.
Discussion. Th e new species is similar to Diplycosia urceolata Stapf from Mount Kinabalu in Borneo, Sabah, Malaysia by its stout glabrous branchlets, coriaceous glabrous leaf blades with rounded apices, and 4-7 mm-long pedicels with a mixture of muriculate trichomes and pale ferrugineous nonglandular trichomes. It diff ers from this species most readily by its green or slightly fl ushed pink petioles 4-7 mm long (vs vivid red and 10-13 mm), wider leaf blades [7-7.5 cm vs (2.5-)3.5-5(-7.5) cm], acute calyx lobe apices (vs obtuse), and lavender mature fruiting calyx (vs black). It is also similar to D. sanguinolenta Sleumer from Mount Kinabalu in its large coriaceous leaf blades [9-14(-17) × 5-8(-9.5) cm for D. sanguinolenta; Sleumer 1967] and generally acute calyx lobes, but is easily distinguished by a petiole 4-7 mm long (vs 12-15 mm) and a white corolla ca. 4.5 mm long (vs bright red and 13-15 mm long), among other characters. Th e new species would key to couplet 3 of the key to the Philippine Diplycosia in Argent (2013). Th e two leads at that point in the key identify the varieties of D. luzonica (A.Gray) Merrill, i.e., D. l. var. calelanensis (Elmer) Sleumer and D. l. var. merrittii (Merrill) Sleumer, distinguished by "Leaves broadly pointed to rounded with the terminal gland forming a short mucronate point the largest leaves up to 5 cm long" vs "Leaves acuminate, with a narrowly acute apex, the largest leaves more than 6 cm long," respectively. Because the new species possesses leaves that are rounded (or strongly emarginate) at the apex but are 8.3-9.7 cm long (the larger ones), the new species does not match either of these leads. Th us, it can be distinguished from all other Philippine Diplycosia by the combination of glabrous branchlets and (larger) leaf blades 8.3-9.7 mm long with an apex that is rounded or strongly emarginate, and with a prominent terminal gland.