Research Article |
Corresponding author: Xun-Lin Yu ( csfuyuxl@163.com ) Academic editor: Jie Cai
© 2019 Lei Wu, Bing-Mou Wang, Bo Pan, Xun-Lin Yu.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wu L, Wang B-M, Pan B, Yu X-L (2019) Spiradiclis tubiflora (Rubiaceae), a new cave-dwelling species from southern China. In: Cai J, Yu W-B, Zhang T, Li D-Z (Eds) Revealing of the plant diversity in China’s biodiversity hotspots. PhytoKeys 130: 217-224. https://doi.org/10.3897/phytokeys.130.34625
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Spiradiclis tubiflora, a new Rubiaceae species, is described from a limestone area of southern China. It is similar to Spiradiclis glandulosa and S. umbelliformis, but differs from the latter two in its linear stipule, short peduncle and tubular-funnelform corolla with a distinctively enlarged tube. The colour photograph, illustrations, detailed descriptions and conservation status of the new species are provided.
Rubiaceae, taxonomy, Guangdong, limestone
Caves are considered to be extreme and exceptional habitats that usually provide insufficient resources, especially lack of light, water and soil for plants to survive (
There are approximately 53 Spiradiclis species worldwide, most representatives being herbs and occurring in limestone areas (
Spiradiclis is a taxonomically difficult genus and most similar to Ophiorrhiza L. (
During a field investigation of the karst cave in Guangdong Province, southern China in 2009, a peculiar species of Rubiaceae was found. The plant has subglobose capsules, dehisces with four valves and many small, granulate seeds when mature (Figs
Materials are deposited at the herbarium of forest plants in Central South University of Forestry and Technology (CSFI), Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences (IBK). Morphological observations and measurements of the new species are based on living material in the field, as well as dry specimens. The conservation status of the new species is evaluated, based on field observations in accordance with
This species is similar to Spiradiclis glandulosa and S. umbelliformis by having procumbent to creeping habit. It is, however, easily distinguished from the latter two by its linear stipule, short peduncle and tubular-funnelform corolla with distinctively enlarged tube.
China. guangdong: Yingde city, Jiulong town, on the wall near the mouth of a karst cave, 460 m alt., 24°17'N, 112°36'E, 18 Oct 2016 (flower), B. Pan GXIBPB2016023 (holotype: IBK!; isotype: CSFI!)
Herbs to 5 cm in height, perennial, procumbent to creeping; stems glabrous or subglabrous. Petiole 0.3–1.8 cm, sparsely pubescent; leaf blade drying papery, adaxially green, abaxially pale, ovate to elliptic, 4.5–25.5 × 4.0–14.5 mm, both surfaces pubescent, abaxially with densely yellow glandule-like spots, base rounded to obtuse, sometimes decurrent, apex acute to rounded; secondary veins 3–5 pairs; stipules usually caduceus, pubescent, narrowly linear, 3–5 mm long. Inflorescences cymose, umbelliform to subcapitate, 2–5-flowered; peduncles 1.2–1.5 cm long, densely pubescent; bracts subulate, densely pubescent, 1.8–3.0 mm long; pedicels 1.5–2.0 mm long. Calyx densely pubescent; hypanthium portion subglobose, 1.4–1.6 mm long; lobes triangular, 1.4–1.6 mm long. Corolla white, tubular-funnelform, subglabrous outside; tube 14–16 mm long, ca. 2 mm in diameter at the base, while 3.8–4.5 mm in diameter at the middle of corolla tube, inside densely pubescent near base; lobes ovate to ovate-triangular, 3.5–4.5 × 2.5–3.0 mm. Stamens 5, inserted at the middle of corolla tube; filaments 0.5–1.5 mm long; anthers dorsifixed, linear. Ovary 2-celled, ovules numerous in each cell on peltate axile placentas, attached to the middle of the septum; stigmas 2-lobed, appearing near the throat of corolla tube. Capsules subglobose, ca. 2 mm in diam., densely pubescent, valves 4. Seeds many, dark brown, granular, 0.22–0.28 mm long.
The new species is only known from the type locality. Plants on the wall or large stones inside or at the mouth of the cave, usually wet and covered with calcareous soil. Flowering from August to October, occasional few individuals in March to May, fruiting from September to December.
The specific epithet refers to the corolla shape of the new species. The Chinese name is given as “cu-tong-luo-xu-cao (粗筒螺序草)”.
Up to now, only one population with 360 individuals have been found in the type locality. Although five field investigations have been carried out in the surrounding area of the type locality in the past five years since the new species was discovered, no additional populations have been found. The individuals are occurring in places with thick calcareous soil and thriving in low-light conditions. Karst caves are known for their spectacular landscape and nature which attract tourists. Many karst caves in China played an important role in stimulating the local economy and were exploited for tourism. The cave where the new species occurred has not been spared and the cement road has been built directly leading into the cave, despite this cave being located far away from human settlements. According to the
The corolla character of Spiradiclis shows great diversity (Fig.
Spiradiclis tubiflora. A Habitat (the arrow shows the place of growth) B Habit C Stipule D Inflorescence, lateral view E Flower, lateral view F Corolla opened to show floral parts G Capsules, frontal view H Capsules, lateral view I Matured capsules with four valves. Flowers of selected Spiradiclis species, lateral views: J S. longipedunculata K S. fusca L S. malipoensis M S. baishaiensis N S. glabra O S. coccinea. Scale bars: 1 cm (B, D, E, F, K, L, M, N, O); 3 mm (C, G, H, I, J). Photos by Bo Pan, Jing Liu and Lei Wu.
Based on our field investigations of Spiradiclis in China and careful studies of relevant literature and specimens, about 94% of the known Spiradiclis species are confirmed to be distylous plant, of which more than 30 species have been observed with both long- and short-styled flowers in the same population. It is known that being distylous is a unique phenotype in plants to ensure reproduction by avoiding self-pollination and to increase male fitness and outcrossing rates by reducing sexual interference between male and female functions (
(Paratypes). CHINA. Guangdong: the type locality, 27 Nov 2016 (fruit), L. Wu & B. M. Wang 5610 (CSFI!), 13 Oct 2017, L. Wu & B. M. Wang 6236 (CSFI!).
Morphological comparison of Spiradiclis tubiflora, S. glandulosa and S. umbelliformis.
Spiradiclis tubiflora | S. glandulosa | S. umbelliformis | |
---|---|---|---|
Stipule | narrowly linear, usually caduceus | deeply 2-parted, persistent | deeply 2-parted, persistent |
Peduncle | 1.2–1.5 cm long | 2–5 cm long | 2–7 cm long |
Calyx lobe | triangular, 1.4–1.6 mm long | oblong-lanceolate, ca. 4–6 mm long | ovate-triangular, ca. 0.6 mm long |
Corolla | tubular-funnelform | funnelform | funnelform to tubular-funnelform |
Corolla tube | 14–16 mm long, enlarged distinctly, 3.8–4.5 mm in diam. at middle | 16–18 mm long, slender, ca. 1.8 mm in diam. at middle | 17–18 mm long, slender, ca. 1.5 mm in diam. at middle |
Authors are grateful to the staff of HN, IBK, IBSC, KUN and PE for permission to examine their specimens. We also thank Zheng-Meng Yang for his excellent drawing and Jing Liu for helping us to prepare the colour figure. This study was supported by the National Nature Foundation of China (project no. 31600160).