A new species of Rigiolepis (Ericaceae: Vaccinioideae) from the Gayo Plateau, Aceh Province, Indonesia

. A new species of Ericaceae from the Gayo Plateau, Aceh Province, Indonesia is described. Rigiolepis gayoensis resembles R. lanceolata but differs by having shorter leaves, non-protruding basal leaf glands, longer flowering pedicels, a glabrous hypan-thium, and a dark red or maroon corolla. A detailed morphological description, ecological notes, conservation status, and photographs are presented. The new species represents the third species of Rigiolepis found in the island of Sumatra. A key to the species of Rigiolepis in Sumatra is provided.


INTRODUCTION
Rigiolepis is a genus of Malesian Ericaceae originally described by Hooker (1873).However, Smith (1935) treated some species of Rigiolepis as belonging to Vaccinium, citing strong resemblance between the two genera.Consequently, as part of Sleumer's (1936) treatment for the Ericaceae of Flora Malesiana, he relegated Rigiolepis as a section of Vaccinium.Argent (2019) later reinstated Rigiolepis as a genus of Malesian Ericaceae through his treatment of Rigiolepis and Vaccinium of Borneo.As per this treatment, including the more recent discovery of R. argentii Mustaqim & Ardi (Mustaqim and Ardi 2021), the number of species recognized for this genus stands at 26. Rigiolepis sensu Argent (2019) is characterized as shrubs, usually epiphytic with a sprawling or hanging habit, with a short corolla (up to 4 mm long or rarely slightly longer), anthers opening by long oblique slits, an inferior ovary that is truly 10-locular, and yellowish or orange immature fruits that turn red at maturity.Rigiolepis has a center of distribution in the island of Borneo, with some species also found in Peninsular Malaysia, including the Indonesian islands of Java, Sulawesi, and Sumatra (Argent 2019;Mustaqim and Ardi 2021).The island of Sumatra is hitherto known as the westernmost distribution of Rigiolepis in Malesia with confirmed occurrence of R. lanceolata (Blume) J.J.Sm.and R. leptantha (Miq.)J.J.Sm.(Sleumer 1966(Sleumer -1967;;Argent 2019;POWO 2023).
During fieldwork in the tropical mountains of Sumatra Island, some unknown specimens of Rigiolepis were documented and vouchered from areas in the midmontane vegetation of the Gayo Plateau, Aceh Province, Indonesia.This region is a component of the northern montane region of Sumatra in Aceh Tengah Regency.The vouchered specimens were examined and compared with those of closely similar species.Relevant literature (e.g., Smith 1935;Sleumer 1936Sleumer , 1961Sleumer , 1966Sleumer -1967;;Vander Kloet 2005;Argent 2019;Mustaqim and Ardi 2021) was also consulted.From the initial data and observation of the plant in situ, we concluded that this plant is a species new to science.

Etymology
The epithet gayoensis is derived from the Gayo Plateau, the name of the area where the species was found.

Phenology
Flowering in June and October; fruiting in January, June, and October.

Distribution and Habitat
Rigiolepis gayoensis is endemic to the Gayo Plateau, Aceh Province, Indonesia (Figure 2).It was observed growing in tropical mid-montane rainforests at 1770 to 1998 m elevation.

Conservation status
Rigiolepis gayoensis is only known from four unprotected areas in the northern Gayo Plateau.All localities are threatened by logging, forest conversion for coffee plantations, and clearing for development and maintenance of provincial roads.However, since the surrounding vegetations of the areas are poorly explored, we believe that other populations can be discovered once botanical explorations are conducted.Here, we provisionally assess the conservation status of R. gayoensis as Data Deficient (DD) (IUCN SPC 2022), as nearby areas with the same elevation and vegetation could harbor additional occurrences of this species.Further detailed population survey highly likely warrant in a threatened status.
Argent (2019) strongly argued for a truly 10-locular ovary for Rigiolepis; a character that greatly supports its generic reinstatement next to Vaccinium.However, previous fieldwork by PWF reveals that Rigiolepis uroglossa has a pseudo-10-locular ovary (P.W. Fritsch, unpubl.data).This character is also observed for R. gayoensis (Figure 1G).Thus, it appears that this character might not be stable to determine generic status of Rigiolepis.Although R. gayoensis would exhibit such placentation, we recognized it as belonging to Rigiolepis through other characters divergent from Vaccinium [i.e., mostly epiphytic or climbing shrubs, rarely > 4 mm long flowers (corolla), yellow or orange immature fruits turning red when ripe].A more detailed morpho-anatomical investigation of the ovary of Rigiolepis across varying stages of development (flower buds to ripe fruits) will be essential in evaluating this crucial characteristic.
In recognizing Rigiolepis as a separate genus, Argent (2019) also used the frequent presence of a fusiform swollen stem bases or roots (vs.usually absent in Vaccinium).Rigiolepis gayoensis possesses a subglobose swollen stem base or root (Figure 3).The function of this organ is likely an adaptation to an epiphytic lifestyle, e.g.storing water (see Harsberger 1908;Benzing 1987).