From 2006 to 2010, Takashige Idei investigated the Mekong river for Cryptocoryne in Thailand, Laos and Cambodia. The results are very impressive. In Aqua Planta 35(4) two new plants are presented. More articles will come in the future.
Cryptocoryne mekongensis differs from all others by having a typical pronounced collar and a rough limb of the spathe with transverse rims. The habitat is the same as for C. crispatula var. decus-mekongensis, at some places they grow together, also with var. crispatula.

Click on the picture to get the full image (ca 50 k)

Low water in the Mekong in southern Laos. photo Idei	Rocky ridges all over. photo Idei	C. mekongensis grows in cracks and between boulders, firmly rooted to survive the high water current. photo Idei	Also sheltered behind the typical willow tree stands. photo Idei
A creek at low water between the many 'islands' in southern Laos. photo Idei	A huge patch of C. mekongensis in Laos. photo Idei	Another habitat is southern Laos. photo Idei	How it looks in the high water season, note the willow tree stands. photo Idei
C. mekongensis from Laos coll. Idei LK5608 photo Idei	This opened spathe has a rather short twist at the top of the limb. Note the transverse ridges on the limb. coll. Idei LK5608 photo Idei	C. mekongensis from Cambodia coll. Idei CKR0104 photo Idei	The limb may be twisted many times more. Note the short tube with a collar. coll. Idei CKR0104 photo Idei
A cultivated C. mekongensis with a far less luxurious foliage. coll. Idei LK5603, cult. B1230	This spathe has a hardly twisted limb of the spathe. coll. Idei LK5603, cult. B1230	A longitudinal section of the spathe. Note the collar. coll. Idei LK5603, cult. B1230	Note also the constricted kettle and the 'roof' above the spadix.. coll. Idei LK5603, cult. B1230
The outer leaves have still the spike form (terete) from the dormant phase. The plant flowers immediately when it starts growing. coll. Idei LK5601,cult NJ photo Jacobsen	A herbarium specimen of C. mekongensis from Cambodia. coll. Idei CKR0104	A sample of alcohol preserved spathe's from a Laos locality of C. mekongensis. coll. Idei LK-G photo Jacobsen	Distribution of C. mekongensis in very east of Thailand, the Champasak province in Laos and the Kratie province in Cambodia

Cultivation of C. mekongensis is easy in loamy sand with or without some peat litter, but it may take an extra year to flower it. In July the plant starts withering, all the leaves will go down in this resting phase and a few spike like leaves develop (in nature it will be submerged). Only in September / October it will thrive again normal leaves. Because of its seasonal character it is not suited for the aquarium.

Updated July 2012

Literature:
Idei, T., J.D. Bastmeijer & N. Jacobsen, 2010. Geschichten vom Mekong: Zwei neue Cryptocorynen (Araceae). Aqua-Planta 35(4): 139-146 (see the Document service, included an English translation)
Mekong River Commission (for water heights and predictions) at: http://ffw.mrcmekong.org/