The south-east asian genus Cryptocoryne has been shown to hybridize more frequently than expected. Data are presented on the known naturally occurring hybrids including information on their discovery, naming, and recognition as hybrids. Many artificial hybrids produced over the years indicate that there are only relatively few barriers to crossing. a heterosis effect is prevalent in many encountered Cryptocoryne hybrids. Vegetative propagation is clearly an advantage in the establishment of hybrid populations and also in detecting the hybrids, since inferior hybrids have disappeared naturally. our results on Cryptocoryne also suggest that when the south-east asian floras become as well-known as temperate ones, the number of natural hybrids will be similar to those presently known from temperate regions.

Chromosome numbers for 38 species of Cryptocoryne are reported, 16 of which have not been reported earlier. About 90% of the species of Cryptocoryne have now been investigated cytologically. On the basis of chromosome numbers, morphology, and distribution, it is possible to distinguish some 24 groups within the species investigated. The chromosome numbers represent a heteroploid series which is based on the (secondary) base numbers 10, 11, 14, 15, 17, and 18. Evidence is given that 2n = 36 is the more primitive one. Evolution on the chromosome level has most likely gone in the direction of a reduction in numbers. Two new species, Cryptocoryne amicorum De Wit & N. Jacobsen and C. keei N. Jacobsen, are described.

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Between March 2006 and February 2015, the occurrence and habitats of the aroid genus Cryptocoryne were investigated in Chiang Khan District, Loei Province, Thailand. In addition to the well-known Cryptocoryne crispatula Engl. var. crispatula and C. crispatula var. yunnanensis (H.Li) H.Li & N.Jacobsen, a recently described species was found: C. loeiensis Bastmeijer et al., as well as a number of plants considered to be hybrids. Although Cryptocoryne is presently abundant, decimation or extinction could occur in the future because of the dam constructions in the Mekong River.