Holotype: Indonesia, W Kalimantan, Schwaner mountains, Sekadau Regency, S of Sekadau, 19 Aug 2015, S. Wongso SW 1561 (BO; isotypes: C, L).
Diagnosis — Cryptocoryne isae usually has fewer than 10 upright leaves to 25 cm long, with a green, narrowly ovate, somewhat spongy blade, which could resemble C. zaidiana; the c. 6 cm long spathe has a short, forward obliquely twisted, purple limb with an indistinct, darker collar, whereas C. zaidiana has a long-tubed spathe with a broad, white, rugose limb and a purple throat. Its chromosome number of 2n = 10 has hitherto not been recorded for Cryptocoryne.
Description — Amphibious herbs, c. 20 cm tall. Rhizome thick, firm, notched, with long, stout, subterranean stolons. Leaves usually less than 10 together in a rosette, 20-25(-30) cm long, blade erect-spreading from an upright petiole, dark green, lighter green abaxially, narrowly ovate, 2-3 × 5-10 cm, thick, softly spongy, smooth, margin entire, smooth or with fine crenulations. Cataphylls whitish brownish, c. 3 cm long, 2-keeled, usually reaching soil surface. Peduncles 1 or 2, to 8 cm long. Spathe c. 6 cm long, whitish outside in proximal part, distal ½ purplish; kettle ovate-cylindric, slightly constricted below level of male flowers, to 2.5 cm long, white inside, flap light yellow; tube c. 1 cm long, white inside; limb forward obliquely twisted, to 3 cm long, purple with an indistinct, darker collar, rather smooth, red colour continuing a few mm into tube. Spadix to 3 cm long, usually with 5 whitish female flowers with broadly ellipsoid to emarginate stigmas with a slight purplish tinge along stigmatic margins; olfactory bodies yellow, rounded; male flowers 30–40, yellowish. Syncarp ovoid with persistent stigmas. Seeds with germinating embryo emerging c. ⅓ from distal end with c. 5 plumulary processes.
Chromosome number — 2n = 10, reported here for SW 1561.
Distribution — Probably endemic to W Kalimantan, Schwaner mountains, Sekadau Regency, S of Sekadau, where it has been observed in one locality besides the type locality.
Ecology — The plants that provided the type specimens were found among other herbs emerging from low-lying forest floor in the upper, drier areas near a stream with a loamy, muddy substrate; the long petiole may be an adaptation to tree leaf accumulation rather than to deep water or substrate sedimentation. The short spathe on a short peduncle situated between the proximal parts of the petioles indicates that plants are always emergent during the flowering season at this site.
A second known locality is reported SW of the type locality. This locality has a higher water level; the peduncle is longer (more than 6 cm). Unfortunately, this site will be opened for agriculture soon. The type locality was also somewhat disturbed, with only secondary forest present. Altitude 125 m.
Eponymy — Named after Isa Bin Ipor, of UNIMAS, who has studied the Cryptocoryne species of Sarawak for many years and more recently has joined explorations for species in Kalimantan.
Remarks — Chromosome number 2n = 10. This surprisingly low number is new in Cryptocoryne. Comparable low chromosome numbers have recently been recorded in the SE Asian Araceae genus Typhonium (Wang & al. 2002; Dao & al. 2007; Sousa & al. 2014).
