Begonia austrovietnamica
Begonia austrovietnamica has been a really rewarding species to grow! I bought one plant from a friend in early fall 2020 and grew it under too-bright lights in my grow tent where I though I could keep it outside a bin, but it soon began to wilt, and the leaves curled significantly. I have since moved it under cover into one of my regular tubs and I use much lower-power lights. Generally, there is little to no air circulation, but I do take the lid off the bin every couple of days for a general bin inspection lasting 15 minutes or so.
This species is from southern Vietnam, as the name implies. The suffix -austro signifies something being southerly-oriented. The leaves are highly textured and dotted sparsely with short trichomes that can be clear or reddish. The abaxial surface is more or less glabrous and ranges in color from tan/beige to scarlet. The petioles have about the same color palette as the leaf undersides but are generally red when fed regularly.
This is a tuberous species and can go dormant if it decides it needs to. If kept too dry, it can trigger this dormancy and you’ll lose pretty much all the leaves overnight. Some folks say it’s good to “cycle” this species (i.e. let it go dry and dormant) once in a while, but I’m yet to try that and I don’t really believe it’s necessary to keep it alive and well.
My largest plant blooms regularly and sometimes will put on more than a dozen inflorescences at once! It appears this species is protandrous (staminate flowers reach anthesis before pistilate flowers) like many other begonias, although some pistilate flowers open and are receptive at the same time as the last of the staminate flowers begin to senesce. An interesting note about the inflorescences themselves- they’re doubly and sometimes triply jointed and flowers arise from each of the joints. I am yet to see pistilate flowers arise from the terminal cluster, they’re nearly always on the bottom joint and occasionally the second.
Propagation is very easy with this species, leaf cuttings root readily in sphagnum or medium-grain hard akadama. Sometimes you can separate a tuber from a larger plant and give it its own space, but several of the leaves will be sacrificed in the process. Seed propagation is very easy, and the fruits develop quite quickly on the plant. Each fruit can contain up to 80 or so seeds that are really pretty large for a Begonia. They’re fast to germinate (average time has been around 8 days) and easy to grow afterwards. I don’t recommend using normal peat to germinate this species, but dried long-fiber sphagnum, fine akadama, and fluval stratum have worked well.
Substrates that have worked for me are very few. So far the mix it has seemed to like best is a 1:1:1 sphagnum / perlite / akadama mix with a few pellets of Osmocote 15-9-12 tossed on top. Long-term akadama made them stall out but that may have been a pH issue. I recommend a slightly acidic medium, and sphagnum seems to be just the trick.
This was once a very, very rare species in the trade but has since become widespread at least with the seasoned terrarium begonia growers. The official species description was published in 2018 by C.-I Peng, C.W. Lin, D.D. Nguyen & N.D. Truong in Phytotaxa Vol. 381. The DOI for the article is 10.11646/phytotaxa.381.1.12
