A Monograph of the Genus Diplycosia (Ericaceae) in New Guinea

Abstract

Diplycosia is an under-studied genus of Ericaceae, with a distribution confined almost to Malesia with most members are endemic to a single island or even a single mountain. New Guinea which, prior to this study, inhabited by 21 endemic species and once considered as one of the centres of diversity. Many species of Diplycosia in New Guinea are known only from limited collections: either only from the type specimens, or from only two or three specimens from a single or few locations; several have incomplete descriptions due to the absence of floral parts. Therefore, a taxonomic revision is needed for the genus Diplycosia in this island. Besides that, despite mostly being narrow endemic, 17 described species have not been evaluated for their IUCN conservation status which has become an obstacle for conservation actions. Therefore, an assessment is urgently required for the genus in New Guinea. A morphological species concept was used in this revision, and specimens were studied from various herbaria either directly or from digital resources: Australian National Herbarium (CANB), Harvard University (A), Muséum National d'Histoire Naturelle, Paris (P), Naturalis History Museum Firenze (FI), Naturalis Leiden (L), Papua New Guinea Forest Research Institute (LAE), PT Freeport Indonesia (tentatively as FRE), Research Center for Biology Indonesia Institute of Sciences (BO), Royal Botanic Gardens Kew (K), and Universitas Papua (MAN). Field explorations were carried out in Indonesian New Guinea, including Birds Head Peninsula and Mount Jaya area. An observation on qualitative anatomical characters of leaf epidermis was done in eight species. Assessment of conservation status was based on IUCN Red List guideline including range sizes calculated using GeoCAT using data sourced from herbarium specimens, literature and recently gathered data from the field exploration. A total number of 26 endemic species are accepted in New Guinea. Four new species are described namely Diplycosia elegans Mustaqim, Utteridge & Heatubun, D. hexamera Mustaqim, Utteridge & Heatubun, Diplycosia puradyatmikai Mustaqim, Utteridge & Heatubun, Diplycosia reticulifolia Mustaqim, Utteridge & Heatubun, together with a variety Diplycosia lorentzii var. acuminata Mustaqim, Utteridge & Heatubun. Diplycosia morobeensis var. ovatifolia Sleumer is reduced to a synonym of Diplycosia morobeensis Sleumer. Based on our current result, a higher number of species was reported from the western half of the island compared to the eastern half. So far, the central part of New Guinea from Jayawijaya Mountains east to the mountains near Indonesia and PNG border is an area with the highest diversity despite being poorly explored. The geographical range of the species varies from widespread species, found across the island, to very narrow endemics, some even restricted to a single mountain complex or a single locality. New Guinean Diplycosia grows as epiphytes or a terrestrial shrubs in mostly the mossy forests upwards to alpine vegetation. The elevation range from 800 in Wandammen Peninsula for D. kosteri and 4000 m in Mount Giluwe for D. rupicola and D. morobeensis. Seven species are known to inhabit alpine vegetation in New Guinea including the new species D. elegans. From this study, we recorded two new important information in the generic character of Diplycosia. It has been recorded from some species that the stamens, especially the anthers are dimorphic, either in length or shape of filaments or anthers. We found that this character is not significant in distinguish Diplycosia to the closest genus Gaultheria. We also recorded the 6-merous flowers for the first time in the genus Diplycosia. Some characters are useful in the identification of New Guinean Diplycosia, including the indumentum on the various organs, leaf morphology, and floral morphology. The use of the fruit characters as an important character has also been recorded in some species which add the value of fruit morphology in Diplycosia identification. In addition, anatomical characters of leaf epidermis sometimes useful in the delimitation of morphologically similar species. Conservation status assessments were conducted for all species with an emphasis on species that have not been previously evaluated. Most of the species are categorized as Data Deficient (DD) with ten species, three species as Least Concern (LC), one as Vulnerable (VU), eight as Endangered (EN) and five as Critically Endangered (CR). The five species categorized as CR are D. hexamera, D. kosteri, D. lorentzii var. acuminata, D. puradyatmikai and D. reticulifolia. Important threats to the extinction of the Diplycosia species in New Guinea come from anthropogenic disturbance and climate change and to a lesser extent natural disaster such as landslides. The anthropogenic disturbance in New Guinea includes habitat conversion for agriculture, mining, road and settlement construction. Illegal logging also has been reported to threaten the epiphytic species. Climate change may cause a negative impact on species that exclusively inhabit the upper elevation of New Guinea ecosystems, such as the montane, subalpine and alpine areas.