Xanthosoma rubrispathum
Helophytic herb, robust, 0.5 - 2.3 m tall, laticiferous, producing white latex when cut. Stem cylindric, 10 - 90 x 9 - 20 cm, covered by shredded leaf bases. Leaves glabrous, 3 - 7 per plant, petioles 40 - 170 x 1.2 - 3.5 cm, green and glaucous, sheath up half of the petiole, sheath usually reddish; leaf blade sagittate 47 - 110 x 43 - 76 cm, glossy to semi-glossy green adaxially, glaucous adaxially, anterior division 35 - 65 x 42 - 66 cm, 1.1 - 1.5 times longer than wide, apex acuminate, primary lateral veins 7 - 10 per side, diverging in a 75 - 85° angle, posterior division 23 - 30 x 43 - 76 cm, basal rib not denuded at all, acroscopic veins 4 - 6, basioscopic veins 8 - 10, apex of lobe round to obtuse. Inflorescences 1 - 3 per leaf axil, peduncle 6 - 16 x 1 - 2 cm, purplish and strongly waxy; spathe 31 - 37 cm long, tube ovoid 6 - 8 x 4 - 6 cm long, purplish red and strongly waxy outside, matte purplish red inside, lamina 21 - 23 x 8 - 10 cm yellowish strongly tinged with red inside, red tinged with purple outside; spadix 26 - 30 cm long, female portion conic, yellow 4 - 5 x 2 - 3 cm, sterile male almost monomorphic, purple, 7.3 - 8 x 1.8 - 2 cm, fertile male portion reddish, 17 - 18 x 1.7 - 2.1 cm. Flowers: female 3 x 2 mm, style discoid and coherent, ovary barrel shaped, 4-loculed, locules 10 - 14-ovuled inserted along the entire flower axis, staminodes elongate towards inflorescence apex, 8 - 10 x 1 mm, synandria 2 - 3 x 4 mm. Pollen grains shed in tetrads. Berry green, 5 - 6 x 2 - 4 mm, seeds 1 x 0.5 mm.
This new species is so far known from a single collection around Manaus, growing along an important road. Since the area is clearly urban, two possibilities can to be considered. The first is that this plant is a relict of the local flora, which has been mostly suppressed only in recent years. The other possibility is that this specimen is from a cultivated origin and was introduced there. Anyhow, even if it is cultivated material, it is not widespread and still needs a Linnean name! Recently, a species of Xanthosoma in cultivation for an equally long time has been officially named for the first time (See Goncalves, 2011). Xanthosoma rubrispathum is similar to Xanthosoma mafaffa Schott, but differs in having the spathe strongly tinged with red (whereas it is only pinkish along spathe margins in X. mafaffa). Basal ribs are usually naked for some extent in X. mafaffa, but it is consistently non-denuded in X. rubrispathum. Major nerves are concolorous with the leaf blade in X. rubrispathum, whereas X. mafaffa has discolorous nerves (always clearer than the leaf blade). In cultivation, X. rubrispathum usually starts to grow with an erect stem, whereas X. mafaffa tends to start with a subterraneous stem and only develop an aerial stem when the plant is much older.