Yangjiang river rug (Cladopus yangjiangensis) from China similar to Cladopus fukienensis and Cladopus austrosinensis

NEWS - Yangjiang river rug (Cladopus yangjiangensis X.T.Liu, G.Di Chen & B.Hua Chen, sp. nov.) from China enriches the understanding of Podostemaceae diversity in East Asia characterized by the longest flowering shoots in the region and exhibiting a large number of elongated leaves per cluster, along with slender roots.

Cladopus is notable for its flat, almost cylindrical or strap-like roots, 4–7-lobed, rough-toed bracts, one or rarely two stamens, and smooth-toed capsules. The genus is found in Southeast Asia, East Asia, Malaysia and Australia. In China, it has been reported from Fujian, Guangdong, Hainan, Guangxi and Hong Kong.

There are likely a total of 10 species worldwide, including Cladopus austrosinensis, Cladopus doianus, Cladopus fukienensis, Cladopus fallax, Cladopus javanicus, Cladopus nymanii, Cladopus pierrei, Cladopus queenslandicus, Cladopus taiensis and Cladopus yinggelingensis.

During a field survey in Yangjiang City in February 2024, researchers discovered a plant in a stream. Upon closer examination, unique features were revealed that suggested it could potentially be a previously unknown species. Comprehensive systematic morphological and molecular analyses confirmed the specimen to be a new species.

C. yangjiangensis shares several similarities with C. fukienensis and C. austrosinensis. However, the leaves of C. yangjiangensis are 18.7–26.7 mm long (vs. 1.3–5.0 mm in C. fukienensis and up to 6 mm in C. austrosinensis). Flowering shoots are 4.2–13.1 mm (vs. 3.5–6.0 mm in C. fukienensis and 1.6–3.5 mm in C. austrosinensis).

In addition, C. yangjiangensis produces more bracts, ranging from 20–54 (vs. 12–36 in C. fukienensis and 8–14 in C. austrosinensis). Roots are much narrower at 0.4 mm (vs. 0.4–1.3 mm in C. fukienensis and 0.5–1.3 mm in C. austrosinensis).

Many other plants grow in the surrounding habitat, including Archidendron clypearia (Fabaceae), Engelhardia roxburghiana (Juglandaceae), Aporosa dioica (Phyllanthaceae), Zanthoxylum avicennae (Rutaceae), Sterculia lanceolata (Malvaceae) and others.

Shrubs include Acronychia pedunculata (Rutaceae), Rhaphiolepis indica (Rosaceae), Rubus leucanthus (Rosaceae), Ficus pyriformis (Moraceae), Glochidion lanceolarium (Phyllanthaceae), Garcinia oblongifolia (Clusiaceae), Melastoma sanguineum (Melastomataceae), Saurauia tristyla (Actinidiaceae), Adina pilulifera (Rubiaceae), Pavetta hongkongensis (Rubiaceae), and others.

Vegetation includes Blechnopsis orientalis (Blechnaceae), Plenasium vachellii (Osmundaceae), Acorus gramineus (Acoraceae), Pandanus austrosinensis (Pandanaceae), Alpinia hainanensis (Zingiberaceae), Thysanolaena latifolia (Poaceae), Miscanthus floridulus (Poaceae), Pentasachme caudata (Apocynaceae) and others.

Some exotic plants include Stauntonia obovatifofoliola (Lardizabalaceae), Phanera erythropoda (Fabaceae), Rourea microphylla (Connaraceae) and others.

The flowering and fruiting season is from November to February the following year. The epithet yangjiangensis (阳江) refers to Yangjiang City, Guangdong Province, South China, where the new species was discovered. Yang Jiang Chuan Tai Cao (阳江川苔草)

The new species is only found in the river in Yangjiang City and researchers suggest the Data Deficient (DD) category of the IUCN (2022). In addition, according to the Updated List of National Key Protected Wild Plants (Decree No. 15) by the country’s State Forestry and Grassland Administration and the Ministry of Agriculture and Rural Affairs, all Podostemaceae in China are classified as national secondary protected species.

DESCRIPTION

Perennial aquatic herb; roots narrowly ribbon-like, compressed, dorsiventral, succulent, ca. 0.4 mm width, 0.1–0.2 mm thick, adhere to the surface of underwater rocks, brick-red during winter, dark green during reproduction; stem short, arising from root branch axils; flowering shoots obpyramidal, solitary, erect, 4.2–13.1 mm tall; leaves linear, in rosette on vegetative shoots, 3–8 in number, 18.7–26.7 mm long, deciduous at flowering; leaves on reproductive shoots palmate (also known as bracts), lobes 3–5 digitate, central lobe long, columns two, opposite, overlapping, bracts 20–54, upper leaves larger, diminishing towards apex, 1.5–1.9 × 1.1–2.0 mm, lobes rigid and coarse after water loss; flowers bisexual, solitary at fertile branch apex, enclosed in pale red spathe during early development; spathella globose, acumen short, 1.7 × 0.3 mm; tepals two, broadly linear, acuminate, 0.7–1.1 mm long; stamen single, 1.2–2.4 mm long; filament nearly cylindrical, slightly flattened, 0.9–1.3 mm long; anthers two, elliptical, yellow, ~ 0.6–0.9 mm long; Ovary single, pale yellow-green, ellipsoid, two-chambered, 1.2–1.7 × 0.9–1.1 mm; ovules ovate, 15–23 per chamber, attached to entire placenta; capsule brownish, globose, smooth, 1.1–1.4 mm long; fruit stalk 1.2–1.7 mm long; seeds small, yellow, narrowly ovoid, 0.3–0.5 × 0.1–0.3 mm.

Original research

Zhang M, Liu X-T, Tian M, Chen Z-X, Huang Y-L, Chen G-D, Chen B-H (2024). Cladopus yangjiangensis (Podostemaceae), a new species from Guangdong, South China, redefining the phylogenetic relationships within Cladopus. PhytoKeys 249: 231-249, DOI:10.3897/phytokeys.249.140342

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