Confusing Thai fruits
This time of the year we have loads of organic fruit ripening at Dokmai Garden: Choganan mango, bananas, pineapple, passionfruit, santol, bignay and unlimited amounts of longan which are so refreshing to eat when chilled in the fridge. We also have another tree fruiting, a tree that has puzzled me for months.
We obtained it as ‘wa’, the Central Thai name for ‘Jambolan apple’ (Syzygium cumini, Myrtaceae). Ketsanee also keeps telling me this is ‘wa’, but whether her Esan ‘wa’ is the same fruit as central Thai ‘wa’ is uncertain.
The jambolan apple is a relative of previously treated rose-, Malay- and Java apple, and the purple fruits of our unknown tree do resemble those of the local Jambolan apple very much. However, the fruits are larger (20 mm instead of 9 mm in Jambolan apple) and the leaves of the Jambolan apple are maximum 13.6 cm, while our tree has 19-23 cm long leaves, not counting the stalk.
An alternative option is Syzygium fruticosum, but that species has normally a brown bark and decurrent leaf margins. Our tree has grey bark and the leaf margins are not decurrent so I reject that option.
A third option is the edible fruit called ‘mah-kiang’ in northern Thai language, Cleistocalyx nervosus var. paniala (Myrtaceae). It is grown commercially in Chiang Mai to make tasty drinks. It has flowers and fruits very similar to those of the Jambolan apple. It is sometimes called ‘wa som’ or ‘wa nam’ which indeed complicates the identification for the innocent home gardener who might be tempted to use a dictionary instead of a flora to identify his fruit. It seems silly that two almost identical plants belong to different genera, but the genus Cleistocalyx has a ring of calyx lobes (sepals) forming a cap covering the flower, while this is not the case in Syzygium. The native C. nervosus var. nervosus has globose fruits, while the originally Indian/Burmese C. nervosus var. paniala and the native Syzygium cumini have elongated fruits.
There are four Cleistocalyx species and 84 Syzygium species in Thailand, all of which are treated by the Flora of Thailand vol. 7:4 (2002). Kew Gardens Plant List do not recognize ‘Cleistocalyx‘ as a valid genus and so Cleistocalyx nervosus var. paniala is named Syzygium nervosum.
Since the Dokmai Garden specimen has the calyx cap, grey bark, 20 mm long elongated fruits (only 8-9 mm long in Syzygium cumini ) and large leaves (much longer than the 13.6 cm which is the maximum length in Syzygium cumini) I conclude this is Cleistocalyx nervosus var. paniala (syn. Syzygium nervosum). I have had great difficulties finding an English name, which is surprising since this fruit is commercially available in Chiang Mai as well as in India, Bangladesh and Burma. ‘Mah-Kiang’ will have to do for the time being. A troublesome fact is that the diameter of this fruit is only 1 cm, while the Flora of Thailand claims it should be more than 1.5 cm, but the author may have compared the diameter of the round fruit of the variety nervosum with the length of the elongated fruit of the variety paniala (Mah-Kiang). I am most eager to get comments on my identification from our experienced readers worldwide so that we can build up a reference collection with confidence.
Text & Flower photos: Eric Danell