Pistia stratiotes

Freitas, Rafaelle Neves, Silva, Maria Francilene Souza, Paiva, Jousimar Silva, Mayo, Simon Joseph & de Andrade, Ivanilza Moreira, 2017, Taxonomic survey of the Araceae Juss. in the coastal region of Piauí state, northeast Brazil, including the Rio Parnaíba Delta, Iheringia, Série Botânica 72 (3), pp. 341-350 : 344-345

4. Pistia stratiotes L., Sp. Pl. 2: 963, 1753. ( Figs. 1 O-S, 2D)

Small, free-floating, densely pilose aquatic plant, becoming fixed in shallow water, 7.9-13.5 cm tall, main stem very reduced, producing slender stolons; roots forming a pendent, feathery mass from the plant base with abundant secondary branching, white and brown; stolons 2.6-10.1 cm long, pilose, leafless, light green. Leaves simple, in rosettes, spongy, subsessile; petiole 1-3 cm long, white; leaf blade 2-6 × 1.5- 2. 8 cm, obovate-oblong, apex rounded to retuse; primary veins 5-8, parallel and distinct, prominent on the abaxial surface. Inflorescence solitary in the leaf axil, erect to suberect, very small and much shorter than leaves, 5-7 per plant, 0.9-1.6 cm long; peduncle 3-6 mm long. Spathe pubescent on both surfaces, constricted centrally, 6-10.1 × 6-8 mm, basal part adnate to the ovary, then margins free and strongly lobed inwards forming a central open chamber around the stigma and an upper expanded lamina around the male zone, lamina ovate, expanded, whitish-green, white on inner surface, apex acuteacuminate, recurved. Flowers unisexual, perigon absent; upper male spadix zone 2-3 mm long, consisting of a whorl of ca. 5 male flowers borne on a short white axis, surrounded at the base by a thin, green, lobed, glandular flap, each male flower consisting of a yellow synandrium of 2 connate stamens; lower female zone consisting of a solitary pistil, 5-7 mm long, with a green glandular flap immediately distal to it, ovary 3-4 × 2-3 mm, ovoid, oblique to the axis of the spathe, unilocular, ovules basal, ca. 1 mm long, numerous, style distinct, much narrower than ovary, ca. 2 mm long, curved to become subparallel to spadix axis, stigma subcapitate, slightly broader than style, translucent white. Fruit a thin-walled berry, 5-7 × 3-3.1 cm, ellipsoid, green, dehiscence irregular. Seed 1.2-1.5 mm long, 3-9 per fruit, brown, barrel-shaped, surface reticulate-alveolate.

Phenology: Flowers throughout the year.

Selected material: Ilha Grande: Barro Vermelho, 09.IX.2011, Freitas 35 ( HDELTA); Barro Vermelho , 18. I.2012, fl. and fr., Freitas 48, 49, 50, 51, 52 ( HDELTA); Cal, 13. VI.2012, fl. and fr., Freitas 83 ( HDELTA); São

Vicente de Paulo , 18. I .2012, fl. and fr., Freitas 53, 54, 55, 56, 57 ( HDELTA). Parnaíba : Braço do Rio Igaraçu, 30.XI.2011, fl. and fr., Freitas 36 ( HDELTA) .

Comments: This species, commonly known as “alfaced’água”, occurs in large populations along the margins of rivers, lakes and ponds, and is usually found together with Lemna species. According to local people, the leaf is used as a tea to relieve menstrual pain. It is also used as an ornamental plant, but can be a harmful weed that covers a great part of the surface of still-water bodies and limits the use of water supplies. P. stratiotes is most abundant in very polluted lakes and streams, harbouring large populations of snails. It is a food source for many animals, such as snails, insects, fish and birds and has a great capacity for sewage bioremediation ( Pott et al. 1999).

P. stratiotes occurs throughout the tropics and subtropics ( WCSP 2015).In Brazil it occurs in the North (Acre,Amazonas, Amapá, Pará), Northeast (Alagoas, Bahia, Ceará, Pernambuco, Piauí, Rio Grande do Norte, Sergipe), Midwest (Goiás, Mato Grosso do Sul, Mato Grosso), Southeast (Espírito Santo, Minas Gerais, Rio de Janeiro, São Paulo) and South (Paraná, Rio Grande do Sul, Santa Catarina) ( Coelho et al. 2015).

Figures

Figs. 1A-S. Araceae from the coastal region of Piauí.A-C. Lemna aequinoctialis Welw.; A. Habit,side view; B. Habit, seen from above;C. Frond showing three veins; D-G. Lemna valdiviana Phil. D. Habit, side view; E. Habit, seen from above; F. Frond showing single vein; G. Fruit; H-N. Montrichardia linifera (Arruda) Schott. H. Habit; I. Inflorescence; J. Stamen; K. Stigma see from above; L. Female flower in longitudinal section showing ovule; M. Infructescence; N. Seed; O-S. Pistia stratiotes L. O. Habit; P. Leaf blade seen from above showing venation; Q. Inflorescence; R. Fruit; S. Seed.