15. Polygonum effusum Meisn. in DC., Prodr. 14: 93. 1857.
P.plebejum R.Br. var. effusum (Meisn.) Hook.f., Fl. Brit. Ind. 5: 28. 1886; P.corrigioloides sensu Schiman-Czeika & Rech.f. in Rech.f., Fl. Iran. 58: 73. 1968 p.p. non Jaub. & Spach 1845.
A profusely branched, prostrate annual herb with channelled stem, glabrous, internodes long. Leaves narrowly linear, sessile, up to 20 x 0.2-0.4 mm with indistinct veins. Ochrea membranous ± lacerate. Inflorescence an axillary cluster of 1-3 flowers per cluster. Flowers pedicellate, clearly exserted from the ochrea; pedicel 1.75-2 (-2.5) mm long, articulated, articulation almost in the middle or slightly below the middle of the pedicel. Tepals 5, pink, eventually turning white, all ± equal, c. 1.75 mm long, obovate, rounded. Stamens 8, c. 0.8 mm long. Styles 3 with 3 capitate stigmas. Nuts trigonous, black and shining.
Fl. Per.: March-October.
Syntypes: India Orientalis regno Oude Wall. 1691/3 (K); Kumaon, Strachey & Winterbottom Himal 4.22 (K); Afghanistan, Griffith (G-DC, K).
Grows from plains to 1300 m as a weed of cultivation, along roadside; Distribution: Bangla Desh, India, Pakisan and Afghanistan.
Polygonum effusum Meisn. has usually been considered as an infraspecific taxon of widely distributed species P. plebejum R.Br. Hook.f., l.c. has treated it as a variety of the latter taxon. Subsequent workers also followed Hook.f. Steward (Contr. Gray Herb. 5 (88): 1-129. 1930) reduced P. effusum to the synonymy of P. plebejum and did not even recognize it as a variety. However, P. effusum differs from P. plebejum in number of characters. In P. effusum the flowers are pedicellate, which are clearly exserted from ochreae, all tepals ± equal and obtuse at the apex and the stamens are 8 in number. Whereas in P. plebejum the flowers are almost sessile to subsessile, which are sunken among the ochreae, tepals unequal, outer tepals acute and the stamens are 5 in number. It is therefore evident from the foregoing dicusssion that P. effusum deserves a separate specific status instead of sinking it in the synonymy of P. plebejum.