Mayaca fluviatilis Aublet, Hist. Pl. Guiane, 1775

Su, Fan, Guo, Ya-Nan, Zhou, Xin-Xin & Wang, Rui-Jiang, 2020, Mayacaceae, a newly naturalized family for the Flora of China, Phytotaxa 447 (1), pp. 77-80 : 77-79

Mayaca fluviatilis Aublet, Hist. Pl. Guiane 1: 42, 3: pl. 15. 1775.

Type:— FRENCH GUIANA. Sinemari river, Mahaica , J. B. C. F. Aublet s.n. (holotype P-00680455 , image! , isotypes BM-001191236 , image!; LD, Acc. no. 1742931 ).

Herbs, submerged or terrestrial. Stems usually much branched, decumbent to erect. Leaves narrowly linear-lanceolate to filiform, 3–4 mm × 0.1–0.3 mm, spirally arranged; sessile. Inflorescence of solitary axillary flowers; bracts ovate, ca. 1.0 mm long. Flowers to ca. 6.0 mm in diam.; pedicels ca. 1.2 mm; sepals 3, persistent, lanceolate-elliptic, 3.5–4.5 × 1–1.3 mm; petals 3, lilac but whitish at base, ovate, ca. 2.5 × 1.5 mm; stamens 3, 1.8–2.0 mm, opposite the sepals; anthers yellow, ellipsoid, 0.6–0.8 mm long, basifixed, dehiscing apically; filaments ca. 1.2 mm; style 1, linear, ca. 1.2 mm long, persistent; stigmas very short, ca. 0.1 mm long, 3-fid at apex; ovary unilocular, ellipsoid, parietal placentae; ovules many. Capsules nearly globose to ellipsoid, ca. 2.0× 1.8 mm, brownish. Seeds ca. 0.4× 0.2 mm, ovoid, reticulate-scrobiculate, with obvious embryostegium ( Fig. 1 ).

Distribution: Native to Central and South America, the Caribbean and the United States. Naturalised in Singapore, Sri Lanka ( Yakandawala & Yakandawala 2007) and Australia ( Madigan & Vitelli 2012), as well as in China, the newly recorded country in Asia.

Phenology: Flowering and fruiting in November and December.

Voucher specimens: China. Guangdong province, Jiangmen city, Enping, Datian town , Nan’ao village , 20 November 2019, 22°15′54.15″N, 112°12′31.95″E, elev. 30 m, Su Fan, Zhou Xinxin & Guo Yanan 1669 (IBSC) ; same town, Shadi village, Fengzishan reservoir, 27 November 2019, N22°13′52.99″, E112°14′36.09″, elev. 33 m, Su Fan, Zhou Xinxin & Guo Yanan 1681 (IBSC) .

Discussion: Probably because of the environmental factors in the habitat of the plant, their vegetative and reproductive organs of this naturalized Mayaca fluviatilis are smaller than those from their native areas, e.g., short leaves and pedicels, and small flowering petals and capsules ( Faden 2000). The variable morphology of this widespread species also resulted in many taxonomic problems, which can be deduced from its many nomenclatural synonyms ( Carvalho & Machado 2015).

Invasive risk evaluation: Mayaca fluviatilis can produce young seedlings by both vegetative propagation and seed germination. Its seeds can maintain viability after drying for six weeks and after at least 12 weeks in submerged conditions ( Thieret 1975). Further experiment about the propagation ability of fragmented vegetative parts of Mayaca fluviatilis showed that even the 2 cm fragment of the terminal shoots was capable of developing into a new plant ( Yakandawala & Dissanayake 2010). It can form dense mats to block freshwater ponds, steams and drainage ditches under favourable conditions and might smother and replace native aquatic plant species. This plant has been a pest within parts of its native range, particularly in Puerto Rico and the US (Florida and North Carolina) and it was assessed to be high week risk in Australia ( Csurhes & Hankamer 2016). To control the fast propagation of this aquatic alien plant, it is necessary to remove even the smallest stem fragments from its naturalised habitats, but it is impossible to totally eradicate them once it has been established locally and the effective control, even application of herbicide, remains elusive ( Madigan & Vitelli 2012).

In China, this species is very common in the collection area. The environmental factors in south China are mostly similar to those in its native and other naturalised habitats and can satisfy the propagation and dispersal of Mayaca fluviatilis . Although the impact of M. fluviatilis is negligible since it is restricted to a small area currently, much attention must be paid to the potential threat to local aquatic environment in tropical and subtropical wetlands of China.

Figures

FIGURE 1. Mayaca fluviatilis.A, Habit. B, Flower. C, Stem branch. D, Leaf arrangement. E, Inflorescence position. F, Sepals and petals, adaxial side (left) and abaxial side (right). G, Lateral view of stamens. H, Capsule (left) and longitudinally dissected capsule (right). I, Capsule. J, Seeds.