Causonis sessilifolia Trias-Blasi & G.Parmar, 2021

Trias-Blasi, Anna, Poopath, Manop, Lu, Li-Min & Parmar, Gaurav, 2021, Causonis sessilifolia (Vitaceae), a new species from Thailand, PhytoKeys 185, pp. 55-64 : 55

Causonis sessilifolia Trias-Blasi & G.Parmar sp. nov.

Diagnosis.

Morphologically, Causonis sessilifolia and Causonis japonica (Thunb. ex Murray) Raf. share similarity in possessing 5-foliolate leaves, but the former taxon has sessile leaves and 2-5-furcate tendrils (vs. petiolate leaves and 2-3-furcate tendrils in C. japonica ).

Type material.

Thailand. Northern floristic region: Nakhon Sawan, Muang, Kriangkrai subdistrict, abandoned area at the bridge of Kriangkrai Canal, 15°44'40"N, 100°11'9"E, 23 October 2019, M. Poopath & S. Duangjai 2511 (holotype, BKF! (SN229663 (Fig. 5 )), isotype BKF! (SN229662)).

Description.

Slender herbaceous climber. Stem cylindrical, 2-5 mm diameter, branched, glabrous, young stems purplish-green, hairy with some bent hairs to glabrous; tendril 2-5-furcate, slender, wiry, leaf-opposed, cylindrical, with a straight section, then bifurcating and coiling, 5-10 cm long, glabrous. Leaves compound, pedately 5-foliolate, alternate or opposite; petiole absent, central petiolule 0.5-1.5(-3) cm long, middle petiolules sessile, lateral petiolules 0.5-2 mm long, mostly glabrous, sometimes with bent hairs; central leaflet blade lanceolate to slightly rhombic, 2-5 by 1-2.5 cm, base cuneate; middle leaflet blade lanceolate, 1-3 by 0.5-1.5 cm; lateral leaflet blade lanceolate often with a single asymmetric acute lobe, 0.5-1.75 by 0.2-1.25 cm, base cuneate; margin broadly denticulate, apex acuminate to mucronate; adaxial and abaxial sides glabrous, mid-rib raised on upper surface, each leaflet with 2-5 pairs of lateral veins, if leaflet lobed then lower lateral vein may be more distinct. Inflorescence ramified, interfoliar or pseudo-terminal, mostly dividing dichotomously, with numerous ramifications, 0.7-2 by 1-2.5 cm, lax, erect; peduncle 2-8 cm long, glabrous, pedicel 0.75-2 mm long, glabrous. Buds ovoid, 1-2 by 1-2 mm. Calyx cupuliform, entire, margin sinuate, 0.5-1 by 1-1.25 mm, glabrous, dark red. Corolla petals 4, ovate, 1.5-2 by 1.25-2 mm, apex cucullate, glabrous, dark red. Stamens 4; filaments flattened, broadening at the base, 1 mm long, cream; anthers elliptic, medifixed, 0.5-1 mm long, cream. Ovary adnate to the disc; disc with 4 distinct lobes, cupular, 0.5 by 1.5 mm, glabrous, dark red outside and whitish inside. Style conical, 0.5 mm long; stigma inconspicuous, dark red. Fruit berry, globose, 4-7 mm in diameter, glabrous, smooth, green. Seeds 2, 4-5 by 3 mm, adaxial side with two faces, abaxial side convex and ovate with a linear chalazal knot (Fig. 2 ).

Phenology.

Flowering and fruiting in October.

Etymology.

The specific epithet " sessilifolia " refers to the sessile leaves of the taxon.

Distribution and habitat.

Thailand (Northern floristic region, Nakhon Sawan). Lowland floodplain forest, along the bank of canal in open areas; 30 m alt. (Figs 1 , 3 ).

Conservation status.

This species is only known from the type locality and, therefore, has an Area of Occupancy (AOO) and Extent of Occupancy (EOO) of 4 km2. This suggests that it might be Critically Endangered as the AOO is less than 10 km2 and is only found in one location. The species has been found to grow outside any protected areas and in an abandoned area next to a canal. This could mean the species is more vulnerable than others as it is unprotected. Additionally, all the surrounding areas are used for agriculture and, therefore, it is likely this forested area might also be transformed for this use. Due to this threat, the restricted AOO and number of locations, we think that this taxon could be driven to being Critically Endangered or Extinct in a very short time; therefore, we assess the taxon as VUD2 ( IUCN 2012).

Taxonomic remarks.

Phylogenetically, this pedately 5-foliolate leaved species lies in a clade previously known with species of exclusively trifoliolate leaves such as Causonis trifolia (L.) Mabb. & J.Wen and Causonis maritima (Jackes) Jackes ( Parmar et al. 2021), but C. sessilifolia lacks the petiolate leaves found in C. trifolia and C. maritima . In particular, this species is phylogenetically most closely related to C. maritima (ML BS = 74%; Bayesian PP = 0.99; Fig. 4 ), but morphologically differs from it in having pedately 5-foliolate leaves (vs. trifoliolate), leaves sometimes opposite (vs. leaves always alternate), leaves sessile (vs. leaves petiolate), inflorescence insertion interfoliar (vs. axillary), calyx and corolla glabrous (vs. hairy).

Figures

Figure 1. Map of the specimen collected (black circle).

Figure 2. Causonis sessilifolia A habit B pedately 5 - foliolate leaves C flowers and opposite leaves D fruits. Images: Sutee Duangjai and Manop Poopath.

Figure 3. Causonis sessilifolia. Habitat. Images: Manop Poopath.

Figure 4. Phylogeny of selected species of Causonis including C. sessilifolia, based on the combined chloroplast dataset (atpB-rbcL, trnC-petN, trnH-psbA and trnL-F). Maximum Likelihood bootstrap values and Bayesian posterior probability values are indicated above branches respectively.

Figure 5. Holotype of Causonis sessilifolia.