Spiradiclisdetianensis (Rubiaceae, Ophiorrhizeae), a new species from southwestern Guangxi, China

Abstract A new species of Rubiaceae, Spiradiclisdetianensis is described from a limestone karst area of southwestern China. This new species is morphologically similar to S.cordata and S.spathulata. All of them have rosetted habit and long peduncles, but it differs from the former by the cuneate leaf bases (vs. basally cordate) and much longer corolla tubes (1.8–2.2 cm long vs. ca. 5 mm long), and from the latter mainly by its tubular-funnel shaped corolla (vs. slenderly salver shaped), 4.5–6.8 (vs. 1.5–2) mm in diam, inside throat and corolla densely puberulent (vs. glabrous except a ring of long hairs at the middle). It also resembles to S.tubiflora, but differs clearly by its subrosulate habit (vs. procumbent to creeping), longer leaf blades (7.0–10.5 cm vs. 0.5–2.5 cm) and longer corolla tubes (18–22 mm vs. 14–16 mm). At same time, color photos, illustrations, detailed descriptions and conservation status of the new species are provided.


Introduction
Spiradiclis Blume is a morphological complex genus of Ophiorrhizeae (Rubiaceae). It is usually distinguished from its relatives by the subglobose or linear-oblong capsules with two or four twisted or straight valves when matured (Lo et al. 1983;Robbrecht 1988;Deb and Rout 1989;Lo 1999;Chen and Taylor 2011). In spite of the characteristic capsule form, the monophyly of the genus has been queried based on recent molecular evidence (Rydin et al. 2009;Razafimandimbison and Rydin 2019). Razafimandimbison and Rydin (2019) even reduced Spiradiclis and Keenania Hook.f. to the synonymy of Ophiorrhiza L. However, we find that the relationship between Spiradiclis and its relatives needs further research and thus we prefer to accept the traditional concept of Spiradiclis here, for the unique capsule form of the genus.
Most representatives have a narrow habitat and prefer to grow at wet places on hill slopes or entrances of caves in limestone areas. During a field investigation to the neighboring regions between China and Vietnam in 2013, the second author came across a peculiar population of Rubiaceae. According to its calciphile habitat and rosetted habit, it is easy to associate with Spiradiclis. However, the flower shape of this population is very different from that of the known species of the genus. Its corollas are tubular-funnel shaped, with 1.8-2.2 cm long tubes, sharply shrunken near base, 4.5-6.8 mm in diam. at throat and 1.8-2.5 mm in diam. near the base, while the corollas of the genus are usually very short or slender. Hence, we revisited this population and collected its capsules. Their subglobose shape and dehiscence with 4 valves clearly indicate this population represents a species of the genus Spiradiclis. After careful comparisons with relevant literatures and examining specimens in herbaria, we found that our plant is most similar to S. cordata H.S. Lo & W.L. Sha and S. spathulata X.X. Chen & C.C. Huang, two species of subgenus Sinospiradiclis, but it can be distinguished from the former by the cuneate leaf bases and much longer corolla tubes, and from the latter by its tubular-funnel shaped corolla and without a villous ring inside corolla. We conclude that this population represents an undescribed species and formally treat it here.

Material and methods
Materials are deposited at the herbarium of Forest Plants in Central South University of Forestry and Technology (CSFI) and Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences (IBK) -herbarium acronyms follow Thiers (continuously updated). Morphological observations and measurements of the new species are based on living material in the field and dry specimens. Diagnosis. The new species is similar to Spiradiclis cordata and S. tubiflora, but it differs from the former mainly by the cuneate leaf base (vs. cordate) and much longer corolla tubes (1.8-2.2 cm long vs. ca. 5 mm long), and from the latter by its subrosulate habit (vs. procumbent to creeping), longer and wider leaf blades (7.0-10.5 × 2.0-3.5 cm vs. 0.5-2.5 × 0.4-1.5 cm), more secondary veins (7-10 pairs vs. 3-5 pairs) and longer corolla tubes (18-22 mm vs. 14-16 mm).
Phenology. Flowering March to April, fruiting from May to July. Etymology. The specific epithet refers to the type locality, where a famous attraction, Detian Waterfall, is situated.
Chinese name. 德天螺序草 (de-tian-luo-xu-cao in Mandarin). Distribution and habitat. Until now, only two populations of the new species have been found. They are both known from limestone hills of southern Guangxi. Plants of the new species prefer to grow at humid places at elevation range of 500-800 m, under evergreen broad-leaved forests with tree species of Fagaceae, Lauraceae, Tiliaceae, Theaceae, Myrsinaceae, Magnoliaceae and Sapindaceae.

Provisional conservation status.
During a series of field investigations at the China-Vietnam border over the past ten years (2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019), only three populations of Spiradiclis detianensis have been observed. One site with nearly 59 matured individuals is distributed in Detian Waterfall (type locality), while the other two sites with more than 250 and 114 individuals are in the Longzhou county and Ningming county, respectively. The habitats of the three sites are in good condition and have been rarely influenced by humans. Considering the above, the species can be assigned a status of 'Least concern' [LC] following the guidelines of IUCN (2019).
Discussion. Our unpublished molecular data indicates that Spiradiclis detianensis shows the closest genetic relationship with S. cordata. Both species prefer to grow on limestone hills from southern Guangxi, China, and have similar habit, such as short stems, subrosulate leaves, long peduncles, heterostylous flowers, funnel-shaped corollas and subglobose capsules. However, the former can be easily distinguished from the latter mainly by its leaf blade basally cuneate (vs. basally cordate) and corolla tubes 1.8-2.2 cm long (vs. ca. 5 mm long) (more detailed comparisons are listed in Table 1).
Spiradiclis detianensis is very similar to S. spathulata in morphology, since both have subrosetted habit, obovate-oblanceolate leaf blades, long peduncles and subglobose capsules, but it differs mainly by its corolla tubular-funnel shaped (vs. slenderly salver shaped), 4.5-6.8 (vs. 1.5-2) mm in diam. at the middle and densely pubescence inside corolla near base and densely puberulent above anther and onto lobes (vs. glabrous except a ring of long hairs at the middle) (more detailed comparisons are listed in Table 1).