Phyllagathis elegans Hai L. Chen, Yan Liu & Ying Liu, 2021

Chen, Hai-Ling, Nong, Shi-Yue, Liu, Yan & Liu, Ying, 2021, A new species of Phyllagathis (Sonerileae, Melastomataceae) from Guangxi, China, Phytotaxa 509 (2), pp. 225-232 : 225-231

Phyllagathis elegans Hai L. Chen, Yan Liu & Ying Liu , sp. nov. ( Figs. 2–5 )

Type:— CHINA. Guangxi: Dongxing County, Ma-lu Town, Ping-feng village , Yuan-ling , Shi-men valley , on rocks and along grassy streamside in forests, 400–450 m, 9 September 2020, JHC343 (holotype: IBK ; isotypes: A , IBSC , PE ).

Diagnosis:— Resembles P. ovalifolia in habit, inflorescence type, floral merosity, stamen and capsule morphology, and crystal form (raphides), but differs in the hirsute stem with crooked hairs (vs. retrorse hairs), distally densely (vs. sparsely) leafy branches, and leaf blades 3-veined (vs. 5–7-veined), oblanceolate to elliptic-lanceolate (vs. ovate, oblongovate, or broadly elliptic).

Shrubs 0.2–0.8 m tall. Stems obtusely 4-sided, densely hirsute with 1–1.5 mm long, crooked, multiseriate hairs, and sparsely pubescent with minute, uniseriate appressed hairs, leafless proximally at anthesis, densely leafy distally. Leaves opposite, equal to distinctly unequal in each pair; petioles 0.5–4.5 cm long, pubescent with minute, uniseriate appressed hairs; leaf blades oblanceolate to elliptic-lanceolate, 4.8–14 × 1.1–2.7 cm, papery to submembranous, green adaxially, pale green abaxially, 3-veined, sparsely pubescent with appressed hairs, and setose with one or two rows of ca. 2 mm long, spreading seta between main veins on both surfaces, base cuneate, margin inconspicuously denticulate, ciliate, apex acuminate to attenuate. Inflorescences terminal, umbellate, 4–15-flowered; peduncles ca. 1.5–2.7 cm long, sparsely pubescent with minute, appressed hairs; bracts 4, red, ca. 10 × 5 mm. Flowers bisexual, radial, predominantly 3-merous (216 out of 229 flowers), rarely 4-merous. Pedicels and calyces pubescent with minute, appressed hairs and spreading, uniseriate, glandular hairs. Pedicels 5–10 mm long, 11–14 mm in fruit. Hypanthia funnel-shaped, 5 × 3 mm, pubescent with spreading, uniseriate, glandular hairs. Calyx lobes triangular, 1.5–2 mm long, apically with 1–6 glandular hairs. Petals pink, ca. 7 × 5 mm, ovate-oblong, slightly oblique, apex acute. Stamens 6 or 8, equal to subequal, isomorphic; filaments 6–8 mm long, purplish-red, glabrous; anthers lanceolate, purple, 6–7 mm long, connectives slightly decurrent, forming a minute, sometimes 2-lobed spur dorsally. Ovary locules 3 or 4, apex with a 4-lobed crown. Styles 12–17 mm long. Capsules cup-shaped, ca. 5.5–7 × 5–6 mm, 3 or 4-sided; crown enlarged enclosing an obpyramidal space; placental column unbeaked, 3 or 4-horned; placentas thready. Seeds small, cuneate, ca. 1 mm, brown.

Crystal form:—Fresh leaves and stems were removed from living plants of P. elegans in the greenhouse of Sun Yat-sen University, cleaned, and sectioned using a double-edged razor blade. Sections were mounted in distilled water under a cover-slip, examined using Motic BA410E microscopy and photographed. As shown in Fig. 3G , raphides are present in the leaf tissue of P. elegans .

Distribution and habitat:— Phyllagathis elegans is currently known from Ma-lu town in Dongxing County and Na-suo Town in Fangcheng District, southern Guangxi, China ( Fig. 6 ). It grows on mossy rocks along streams in secondary broadleaf forests at elevations of 400– 550 m.

Phenology:—Flowers, young fruits and old fruits in September.

Etymology:—The specific epithet refers to the delicate and beautifully arranged leaves of the new species.

Additional specimen examined:— CHINA. Guangxi: Fangcheng District (misrecorded as Dongxing County), Na-suo Town, 31 October 1939, S. N. Gan 40111 ( PE) .

Conservation status:— Phyllagathis elegans is currently known from two locations, Ma-lu town in Dongxing County and Na-suo Town in Fangcheng District, southern Guangxi, China. The population in Ma-lu town, which we visited in 2020, comprises ca. 100 individuals scattering along stream banks; the population size in Na-suo Town remains unknown. The new species occurs at low elevations where the risk of habitat destruction by human activities is relatively high. Its area of occupancy (AOO) and extent of occurrence (EOO) are respectively 8 km 2 and 1.475 km 2 (both calculated through GeoCAT; Bachman et al. 2011). Phyllagathis elegans should be considered endangered [EN, B1ab(iii)+B2ab(iii)] according to the IUCN red list criteria ( IUCN Standards and Petitions Committee 2019).

Notes:— Recent revisions adopted a broad generic circumscription of Phyllagathis ( Cellinese & Renner 1997, Cellinese 2002, Cellinese 2003). With continued description of new species (e.g. Wangwasit et al. 2010, Mathew et al. 2016, Lin et al. 2017), the genus now contains over 70 species distributed from southern China, Indochina , western Malaysia to Sumatra and Borneo. Phylogenetic analyses based on nrITS and plastid DNA sequence data both recovered Phyllagathis as highly polyphyletic, encompassing a dozen lineages ( Zhou et al. 2019a, 2019b). One of these lineages, viz. unnamed clade 1 ( Zhou et al. 2019b), comprises at least ten species from southern China, Vietnam and Borneo. Species in this clade are characterized by the caulescent habit, ovate, elliptic to oblong-lanceolate leaves, umbellate or cymose inflorescences, isomorphic stamens, dorsally spurred connectives, enlarged ovary crown, horned placental column, and thready placenta ( Zhou et al. 2019a, 2019b). In addition, some species in this clade, such as P. ovalifolia , have raphides which are rarely recorded in Sonerileae ( Van Vliet et al. 1981, Hansen 1992, Mentink & Baas 1992). Phyllagathis elegans closely resembles species of the unnamed clade 1 in morphology, crystal form and geographic distribution ( Figs. 2–6 ) and could be a potential member in this clade. As this clade showed no close relationship with the type of Phyllagathis , it was suggested that is should be excluded and treated as a distinct genus ( Zhou et al. 2019a, 2019b). However, no formal treatment has been made to date. Therefore, we describe P. elegans as a member in Phyllagathis as defined by Cellinese (2002, 2003).

Figures

FIGURE 2. Phyllagathis elegans, all from JHC343 (A, IBK, IBSC, PE). A. Habitat. B. Flowering branch. C. Crooked hairs on the stem. D. Top to bottom, lateral, adaxial, and abaxial views of leaf, showing the bristles. E. Young inflorescence, showing the red bracts (one removed). F. Mature inflorescence.

FIGURE 3. Phyllagathis elegans, all from JHC343 (A, IBK, IBSC, PE).A. Top view of a flower.B. Side view of a flower. C. Longitudinal section of a flower showing subequal stamens. D. Anther morphology in detail. E. Top view of young capsules. F. Longitudinal section of old capsule showing the enlarged ovary crown, horned placental column, and thready placentas. G. Crystals in the petiole (raphides). Scale bars: 5 mm (A–D, F), 50 μm (G).

FIGURE 4. Line illustration of Phyllagathis elegans. A. Habit. B. Top to bottom, adaxial and abaxial views of a leaf. C. Left to right, side and top views of a flower. D. Longitudinal section of a flower. E. Side view of a flower with petals and stamens removed, showing hypanthium and calyx lobes. F. Petals. G. Top to bottom, longitudinal section of 4-merous and 3-merous capsules.

FIGURE 5. Holotype sheet of Phyllagathis elegans.

FIGURE 6. Distribution of Phyllagathis elegans and P. ovalifolia.