Melastoma candidum D. Don, 1823

Zhang, Xinjian, Dai, Jin-Hong, Liu, Xiaozhou, Li, Zihua, Lee, Shiou Yih, Zhou, Renchao & Tan, Guangwen, 2020, Lectotypification of the name Melastoma candidum f. albiflorum and its taxonomic status, PhytoKeys 146, pp. 47-52 : 47

Melastoma candidum D. Don

Synonym.

Melastoma candidum D. Don f. albiflorum J. C. Ou.

Lectotype

(designated here): - China. Taiwan. Ilan, Yuensanhsiang, leg. Jun-Chih Ou 64, July 6, 1976, Herbarium of National Research Institute of Chinese Medicine (HNRICM!).

Description.

Perennial shrubs, 0.3-1.5 m tall. Twigs nearly 4-angled to subterete in the younger parts and terete in the old parts, densely covered with appressed to suberect strigose with scales. Leaf blades ovate to elliptic, papery, 3.3-4.8 × 6-9.5 cm, base broadly cuneate to rounded or subcordate, apex acuminate, margin entire, palmately 7-nerved (the marginal nerves often inconspicuous), adaxially densely strigose, abaxially densely puberulous, strigose along veins; petioles 1.4-2.0 cm, densely strigose with scales. Inflorescences subcapitate corymbose, terminal, 3-5-flowered, with 2 leaf-like bracts at base. Pedicels 8-12 mm, densely strigose with scales; bracteoles 2, opposite, elliptic-lanceolate to elliptic, 6-13 mm, abaxially densely strigose, margin ciliate. Hypanthia 7-12 mm, densely appressed-strigose with scales, margin fimbriate. Sepals lanceolate to ovate-lanceolate, apex acuminate, densely strigose and pubescent on both sides and along the margin. Petals 5, occasionally 6, white, obovate, ca. 27 × 18 mm, apex rounded. Stamens 10, dimorphic, longer stamens with anthers linear, curved, ca. 9 mm, filaments ca. 10 mm, joined by a connective ca. 9 mm, curved, spur bifid ca. 2 mm, shorter stamens with anthers ca. 8 mm, 2-tuberculate at base, filaments ca. 7 mm, without prolonged connective. Ovary half-inferior, campanulate, with a ring of bristles at apex. Capsule dry, urceolate, apically dehiscent, 9-16 × 7-10 mm, densely squamose strigose. Seeds numerous, minute, cochleate. Fl. May-Aug, fr. Aug-Oct.

Distribution and habitat.

The white-flowered form of M. candidum was first reported only from Hsinchu Hsien and Ilan Hsien (Taiwan). This form has also been reported to occur in the Ryukyu Island ( Hatusima and Amano 1994), but without exact specimen information. The individuals in Fujian, China represent the first known occurrence of this form outside of Taiwan Island (Fig. 2 ). It occurs only in lowland evergreen forest margins at an elevation of approximately 150-300 in Pinghe County, Fujian. They occur in evergreen forests dominated by Blechnum orientale , Dicranopteris pedata , Miscanthus floridulus and Rhodomyrtus tomentosa .

Notes.

The key character of the white form of M. candidum is its white-colored flowers, which can be easily distinguished from the purple form of M. candidum . Whereas the purple form has a relatively wide range of distribution in northern Vietnam and southern China ( Liu et al. 2014), the white-flowered individuals have been found across a narrow region. Individuals in Taiwan and mainland China may represent independent origins of white petals from local populations of M. candidum , since breakdown of the anthocyanin synthesis pathway in plants is relatively common ( Smith et al. 2012; Zheng et al. 2019).

The flowers of the white form of M. candidum have been used in folk-medicine for the treatment of hypertension, dysentery, diarrhea and antibacterial ( Chou and Liao 1982). During our survey, we also learned that the white form has been cultivated as a medicinal herb by the local people in Pinghe County, Fujian. They believe that it is highly effective for the treatment for nephritis, and has led to the exploitation of natural populations, threatening its survival in the wild. Due to its narrow geographical range and small population size, effective conservation effort is required.

Paratype.

- China. Fujian Province, Pinghe County, in lowland evergreen forest margins, 24°02.66'N, 117°04.75'E, Elev. 276 m. 28 July 2019, X. J. Zhang, ZXJ-1901 (SYS)

Figures

Figure 2. Distribution map of the white form of Melastoma candidum. Square (■) represents previously reported localities, solid circle (●) represents newly recorded locality. Map was created using SimpleMappr, http: // www. simplemappr. net (Shorthouse 2010).