Holotype: Indonesia, W Kalimantan, Schwaner mountains, Sintang Regency, S of Sekadau, 18 Aug 2015, S. Wongso & I. B. Ipor SW 1560 (BO; isotypes: C, L).
Diagnosis — Cryptocoryne erwinii superficially resembles C. lingua in the leaves, but the leaf blade is more horizontally oriented, with the abaxial surface distinctly lighter than the adaxial one. The 6–9 cm long spathe is exceptional and differs from all other Cryptocoryne species in being white, with the distal part of the limb subulate and purple inside, first bent backward to upright, later bending forward over the white, widely expanded, funnel-shaped entrance, which lacks a collar. Its chromosome number of 2n = 26 has hitherto only been reported for the recently described C. aura.
Description — Amphibious herbs 8–10 cm tall. Rhizome thick, stout, notched, with long, stout subterranean stolons. Leaves 5–10 together in a rosette, 6–10 cm long, blade spreading ± horizontally from upright petiole, green adaxially, lighter abaxially, ovate, to 3 × 6 cm, superficially smooth but with small rounded protuberances, base slightly cordate. Cataphylls greenish, to 2 cm long, 2-keeled. Peduncle 1–2 cm long. Spathe 6–9 cm long, red-brownish outside; kettle white inside, cylindric, with a broad constriction at middle, 1.5–2.5 cm long, flap white; tube 2–4 cm long, twisting after opening; limb subulate, 2–3 cm long, backward bent to upright at opening, next day bending forward, protecting opening of white, expanded funnel-cone-shaped tube opening (unusual tube opening may originate from a collar that has expanded and formed dilated opening). Spadix 1.5–2.5 cm long, with 4 or 5 white female flowers with broadly ellipsoid stigmas; olfactory bodies yellowish white; male flowers 30–40, yellowish; appendix white. Syncarp not observed.
Chromosome number — 2n = 26, reported here for SW 1560.
Distribution — As far as known endemic to W Kalimantan, Schwaner mountains, Sintang Regency, SW of Sintang, where it has been found only at the type locality.
Ecology — The type specimen was collected in a small humus-rich muddy-peaty streamlet in a swamp forest, where the population was growing among tree roots. The habitat conditions indicate that the water flow is constantly low so that dead leaves accumulate to form a muddy-peaty, loose, organic substrate. Water parameters: pH 5.5, conductivity 25 µS/ cm, temperature 25°C. Altitude 60 m.
Eponymy — Named after Erwin Syahputra, who has a keen eye for plants, and discovered the habitat of this unique species.
Remarks — The colour and structure of the spathe of Cryptocoryne erwinii is unique, no other species having anything like the limb of this species. The chromosome number of 2n = 26 is the same as that found in C. aura, but the morphology of the two species is very different.