Cyrtandra argentii, a new species of Cyrtandra (Gesneriaceae) from the Philippines, and a review of the C. villosissima group

Cyrtandra argentii Olivar, H.J.Atkins & Muellner sp. nov., endemic to the Philippines and named after George Argent, is herein described and illustrated. Collections associated with this new species are often confused with three other species, namely C. ferruginea Merr., C. villosissima Merr., and C. hirtigera H.J.Atkins & Cronk. Distinguishing characters including keys, updated descriptions, distribution maps, and photos of live specimens are provided to aid identification of the four species. Following the International Union for the Conservation of Nature (IUCN) criteria, C. argentii sp. nov. is considered to be Near Threatened (NT) due to its distribution in a zone susceptible to anthropogenic pressure and the lack of any formal protection.


Introduction
Cyrtandra J.R.Forst. & G.Forst. (Forster & Forster 1775) is the largest genus of ca 800 spp. in the family Gesneriaceae Rich. & Juss. (de Candolle 1816). The genus is recognized by possessing two fertile stamens and fruits that are indehiscent, either hard capsules or fl eshy berries (Cronk et al. 2005;Atkins et al. 2013). Members of the genus exhibit diverse growth forms, ranging from herbs and shrubs, to climbers and small trees distributed throughout the Malesian region and across the Pacifi c Kartonegoro et al. 2018). Species of Cyrtandra are important rainforest elements, thriving in habitats with high humidity, low light intensity, and constant moisture supply (Gillett 1967). Despite a continuous distributional range, the genus shows high levels of local endemism exhibiting high degrees of ecological specialization, making it an ideal candidate to address hypotheses on speciation, patterns of diversifi cation, and community assembly Bramley et al. 2004;Clark et al. 2009;Johnson et al. 2019).
In recent years, several studies (Wagner et al. 2001;Bramley et al. 2003;Atkins 2004;Bramley 2005;Lorence & Perlman 2007;Bone & Atkins 2013;Johnson 2017;Kartonegoro et al. 2018;Atkins et al. 2019;Nishii et al. 2019) have led to an increase in numbers of species of Cyrtandra. These studies emphasized the urgency to document and understand the biodiversity of cyrtandras before they succumb to anthropogenic pressures. However, little is still known about the taxonomy of members in areas which are considered centers of biodiversity for the genus. Atkins et al. (2013) estimated a high species richness on Borneo, in the Philippines and on New Guinea. Understanding species boundaries of members from these areas is becoming increasingly important for examining biological trends of adaptation and speciation, and facilitating ecosystem and species conservation assessments.
For the Philippines, a comprehensive account of Cyrtandra spp. was published by Merrill (1922) in his An Enumeration of Philippine Flowering Plants noting 83 species, of which only C. oblongifolia C.B.Clarke (de Candolle & de Candolle 1883) was listed as not endemic.  revised Philippine cyrtandras from the island of Palawan, describing seven new species and indicating that C. elatostemoides Elmer (Elmer 1913) is also found on Borneo. Both accounts were considered in an updated checklist of Philippine cyrtandras available through 'Co's Digital Flora of the Philippines' (Pelser et al. 2011 onwards). A taxonomic revision of Philippine cyrtandras, however, addressing species boundaries, distributions, and descriptions is yet to be achieved.  noted the striking vegetative similarities between C. villosissima Merr. (Merrill 1906) from the island of Mindanao and a 1922 collection by Merrill from the island of Palawan which he labeled C. woodii Merr. ined. with no accompanying publication. Similarities include an erect suffrutescent habit, and large leaves that are slightly falcate and densely hirsute. However, in Merrill's 1922 Enumeration of Philippine Plants the name C. woodii did not appear, and the distribution of C. villosissima was extended to Palawan, which according to  seems to provide evidence for Merrill's decision to 'sink' his C. woodii into C. villosissima. Increased sampling in the locality of C. woodii led to collections with reproductive structures that show the species' distinctness from C. villosissima. This ultimately led to the description of C. hirtigera H.J. , favoring a new name to prevent confusion with the Bornean C. woodsii B.L.Burtt (Burtt 1970). In the course of an ongoing research project, aimed at the taxonomic revision of Philippine cyrtandras, it was found that C. ferruginea Merr. (Merrill 1915) and a series of collections from Mindoro and the Aurora Province housed at the Royal Botanic Garden Edinburgh (RBGE) share similar vegetative characters with C. villosissima. As a result, identifi cation of several herbarium specimens was found to be intermediate between C. villosissima and C. ferruginea, without a clear distinction being possible between the two when no additional reproductive characters were present. In this paper, species sharing the character combination of an erect suffrutescent habit and large leaves that are slightly falcate and densely hirsute, are referred to as the C. villosissima group. Members of this group are C. ferruginea, C. hirtigera, C. villosissima, and C. argentii sp. nov. Our study aims at clarifying the differences between these species through keys and photographs, and provides a description and diagnosis for a new species often misidentifi ed as either C. ferruginea, C. villosissima, or C. hirtigera.

Material and methods
Data for this study were derived from herbarium specimens including their corresponding fi eld notes, photographs, and fi eld observations. Whenever available, living collections housed at the Royal Botanic Garden Edinburgh (RBGE) were consulted and reproductive characters and measurements were recorded from material preserved in alcohol. All Philippine Cyrtandra deposited at AAH, BM, BO, E, GH, K, L, NY, P, PNH, and US were consulted through visits to these herbaria and access to digital images. Herbaria acronyms follow Index Herbariorum (Thiers, continuously updated). Descriptions follow schemes of recently published accounts of new species Johnson 2017;Kartonegoro et al. 2018;Atkins et al. 2019). Assessment of Conservation Status was implemented using GeoCAT (Bachman et al. 2011), following the IUCN Red List Category criteria (IUCN Standards and Petitions Subcommittee 2017).

Results
Cyrtandra ferruginea, C. villosissima, C. hirtigera, and the new species described here share the following characteristics: erect suffrutescent habit and large slightly falcate and densely hirsute opposite leaves. There exist minute differences in their vegetative characters and they are presented in the key. Table 1 details more differences between the studied species. The studied species primarily differ, vegetatively, in color of indumentum and leaf symmetry. Cyrtandra argentti sp. nov. is distinct among the three species by having a white indumentum, and C. ferruginea is distinct by having pronouncedly anisophyllous leaves. Ultimately, the species are distinguishable by calyx and infl orescence type, corolla color and, to some degree, by geographic distribution (Fig. 1). Cyrtandra hirtigera is restricted  (Forster & Forster 1775) Key to the studied species

Diagnosis
The species' pendulous compound cymose infl orescences (10-15 fl owers) distinguish it from all other members of the genus in the Philippines. The combination of subequal leaves, white woolly indumentum, glabrous corolla, and ovoid fruit separates this species from the rest of the C. villosissima group.

Etymology
This species is named after George Argent who was part of the team that collected specimens at the type locality. George's contribution to our knowledge of the Philippine fl ora is undisputed. His extensive fi eldwork in the country has led to the discovery of several new species, recognition of important conservation areas, and promotion of biodiversity studies.

Distribution and habitat
Cyrtandra argentii sp. nov. is found growing on slopes near streams in primary forests. This species is distributed from the north of Luzon to the island of Mindoro.

Conservation status
Cyrtandra argentii sp. nov. occurs at an elevation of 600-800 m a.s.l. which corresponds to the forest land use zone (Villanueva & Buot Jr 2018). Using the online GeoCAT conservation assessment tool (http://geocat.kew.org/), the proposed conservation category based on Extent of Occurrence (EOO) is Near Threatened (NT), and the category based on the estimated Area of Occupancy (AOO) calculated using the default 2 × 2 km grid is Endangered (EN). Here, we consider this species' status as NT due to: i) its occurrence in close proximity to the agroforest land use zone, the latter at approximately 100-400 m a.s.l. (Villanueva & Buot Jr 2018); and ii) the fact that the forest areas wherein the species occurs are not declared protected by law (Biodiversity Management Bureau 2015), making it highly susceptible to population decline through deforestation and other anthropogenic activities.

Notes
Like many species of Cyrtandra, fi laments of C. argentii sp. nov. recoil into the corolla tube after anther dehiscence. This is hypothesized as constituting a mechanism against self-pollination (Bramley et al. 2003). The length of the style also varies developmentally, the style can be either exserted or inserted depending on the stage of maturity of the fl ower.

Distribution and habitat
Cyrtandra ferruginea is found growing in damp forests at approximately 500-800 m a.s.l. and can be found on Catanduanes, Mt Isarog, Mt Mayon, Mt Malinao and Mt Bulusan (Fig. 1).

Notes
Cyrtandra ferruginea is morphologically most similar to C. argentii sp. nov., but can be separated by the following characters: ferruginous anisophyllous leaves, 1-3 fl owered simple cymes, and hirsute corolla.

Distribution and habitat
Cyrtandra hirtigera is distributed throughout the island of Palawan and is usually found on slopes near gullies at 30-900 m a.s.l.  described two varieties of this species, C. hirtigera var. hirtigera and C. hirtigera var. chlorina, distinguishable by color and shape of their calyces and corolla limbs. Cyrtandra hirtigera var. hirtigera has a crimson indumentum, red calyces with acute lobe apices, and reddish orange corollas with slightly bilabiate limbs. Cyrtandra hirtigera var. chlorina has pale indumentum, green calyces with acuminate lobe apices, and yellowish green corollas with subequal lobes.

Distribution and habitat
Cyrtandra villosissima is distributed throughout the island of Mindanao and extends to the island of Negros in the Visayas and is usually found in well-shaded areas near ravines.

Notes
Cyrtandra villosissima is vegetatively similar to C. hirtigera. It is distinguishable by its red corolla and green calyces with distinctly linear lobes. Based on available distribution data, C. hirtigera appears to be restricted to the island of Palawan while C. villosissima can be found from Negros Island to the island of Mindanao.

Discussion
The recognition of C. argentii sp. nov. as a new species was here aided by increased availability of collections with reproductive parts and continued alpha-taxonomic work. This highlights the importance of reproductive characters in establishing species boundaries among Cyrtandra species. In phylogenetic analyses of the Southeast Asian Cyrtandra (Atkins et al. 2020), the C. villosissima group was not resolved as monophyletic; only C. villosissima and C. hirtigera belonged to the same subclade, but were not resolved as exclusive sister taxa. The character combination of erect suffrutescent habit with large leaves that are slightly falcate and densely hirsute has evolved at least three times independently (Atkins et al. 2020). Figure 3 shows this shared character combination and Fig. 4 shows the infl orescence type that ultimately distinguishes the species from each other.
The genus Cyrtandra is the most taxonomically challenging in the Gesneriaceae due to its large number and high proportion of poorly known and undescribed species (Burtt 2001;Atkins et al. 2013;Clark et al. 2013). Atkins et al. (2013) estimated 800 species of Cyrtandra. Since then, several authors (Bone & Atkins 2013;Johnson 2017;Kartonegoro et al. 2018;Atkins et al. 2019) have described additional species. The number of species is expected to increase further as more alpha-taxonomic work and fi eld collection are carried out.
Large genera can be systematically addressed by following a phylogenetically informed taxonomic approach on a region-by-region basis Clark et al. 2013). This has been applied effectively by Bramley (2005) in a revision of Cyrtandra section Dissimiles in Borneo. The approach involves a robustly sampled phylogenetic tree wherein monophyletic clades can be characterized morphologically by one or more salient characters Clark et al. 2013). Taxa with molecular data can be assigned to the clades while taxa lacking molecular data can be tentatively assigned based on morphological similarities. Upon assignment to a clade, taxonomic assessment can be streamlined by focusing on related taxa identifi ed through both morphological and molecular data, therefore limiting the number of potential conspecifi cs for comparison. Areas, particularly archipelagos, with high diversity can benefi t from this approach since it provides a systematic way of prioritizing areas where additional fi eldwork and alpha-taxonomic work are most needed. Clark et al. (2013) suggest that phylogenetically defi ned areas can be addressed taxonomically fi rst, followed by increased sampling in lesser-resolved areas. This strategy is currently being applied to study the genus in the Philippines with the aim of producing a complete revision of Cyrtandra in the archipelago (Olivar et al., in preparation).