Cryptocoryne cordata siamensis
The form of C. cordata occurring in Thailand.
Karyotype: 2n=68, 2n=102

Jan Bastimeijer and Joseph Bogner weighed in on C. cordata and using karyotype (= number of chromosomes) evidence have made a significant and sensible - given what we know - reclassification; there are still forms that have not gone expensive DNA analysis yet and almost certainly more forms of this highly variable plant still to be found.

So, the new breakdown goes like this:

Cryptocoryne cordata siamensis Aquarium strains
Aquagreen Oriental
blassii siamensis

SIA - Crypt. cordata siamensis Unknown aquarium strain

Cryptocoryne cordata siamensis Loc: KR01

SIA - Crypt. cordata siamensis KR01

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Neils Jacobsen and Joseph Bogner collections.

Cryptocoryne cordata siamensis var. 'Rosanervig'
emerse flower
fruit submersed

SIA - Crypt. cordata siamensis 'Rosanervig'

This cultivar showed up in a commercial shipment in the 1970s and was finally located in nature in Thailand around 2010. It's been shown (Eggler 2019, Wongso 2019, pers comms) that reduced illumination is a prerequisite for the famous veination pattern to display. In higher light they look like any other Crypt. cordata siamensis plants. The flowers are not unusual in any way, just the leaves.