A few days ago I liberated the tall and handsome spiral gingers (Cheilocostus speciosus and C. lacerus) from a bunch of vines. Among the usual weedy vines (Centrosema pubescens, Hewittia malabarica and Paederia foetida) was a fourth trailing weed which I did not recognize straight. Visiting friends from Australia asked me about it so I dedicate this blog to them.
One of the Australians, a certain Mr Darcy Duggan has a thorough life experience from national park and state park work in Melbourne. As a teacher for new national park rangers he was told to scrap the excursions of economical reasons, and to replace the field studies with ‘computers’. Mr Darcy was shocked, he realized the administrators did not have a clue about what biology is, and since he realized he could no longer use the most powerful pedagogic tool to teach botany he simply quit. Only a very strong man can leave his job and income because he deems he can no longer fulfill his duty. I think of Jane Austen’s gentleman ‘Mr Darcy’. Our Mr Darcy has already left Dokmai Garden for China, but if we are lucky we can lure him back to give a talk later this year.
To further illustrate what a poor substitute computers are compared to field studies, let’s go back to that obscure plant. Having years of field experience enables any field botanist to quickly exclude what species it can not be and what family of plant it may be. An experienced botanist also uses books written by authorities, rather than browsing the internet for articles written by amateurs copying each other’s mistakes.
In this case a quick look in Radanachaless & Maxwell (1994) ‘Weeds of soybean fields in Thailand’ hinted at the ‘desert horse purslane’ (Trianthema portulacastrum, Aizoaceae). My notes in pencil said this species without flowers may resemble the hog-weed Boerhavia diffusa of the Nyctaginaceae family, also included in the book. In fact, these plants may resemble each other so much that even the Thais use the same vernacular names for both of these unrelated plants (phak khom hin, phak bia hin). A striking feature is the pair of leaves of unequal size, but the flowers are very different and they are unstalked in desert horse purslane but with long stalks in Boerhavia. If you Google these scientific names, you end up with so many pictures of so many different plants you get very confused.
Thanks to the field notes in the margin we had homed in on both family (Nyctaginaceae, the Bougainvillea family) and genus (Boerhavia). I am familiar with Boerhavia diffusa, which also grows at Dokmai Garden and usually has very long and branched flowering stalks, and is a relatively small weed, while the plant at hand has much shorter and unbranched flowering stalks and the whole plant is more fleshy, larger and clearly crawling over other vegetation.
A quick look in Flora of Thailand 5:3 (1992), which is the authority used by all field biologists in Thailand, revealed that the author Professor Kai Larsen selected three species, but he commented that “A very large number of species have been described, but here a more conservative species concept has been applied”. B. chinensis has heart-shaped leaves and funnel-shaped flowers, while the plant at hand has bell-shaped flowers and oval leaves. Only B. erecta remains, which Larsen considers a rare species not reported from Chiang Mai, and similar to B. diffusa but different in number of stamens and the shape of the minute fruit. This makes one wonder if there is another species untreated? Tem Smitinand’s plant list (2001) is therefore a good source. He only adds B. repanda, which Flora of Thailand claims is synonymous with B. chinensis.
I checked the synonyms of B. diffusa as listed by Flora of Thailand, and there are both B. repens and B. procumbens, both names suggest a crawling or trailing habit like the plant in our hand. Instead of googling these names which I am sure would result in pictures of many unrelated species, I walked out in the garden at night with a torch to make a moonlight field study. I compared the typical B. diffusa which grows in sunny areas with low and sparse vegetation, and the crawling thick undetermined Boerhavia which grows in moister and more shady areas with a thick mass of other weeds. Indeed, there is a continuum of plant forms between the two habitats, so the unknown plant is also a hog-weed!
Now, are computers all useless in botany teaching? Of course not; like this blog they may help and stimulate you to embrace your garden and nature, and some books, scientific articles and species descriptions are easily available on-line. Computers and books are good additions to field studies, but you need to have the experience of the variation of a plant due to season, habitat and age, and you need to touch, taste and smell, and see it in its native environment with its soil and accompanying plants, degree of shade and moisture.
Walking with an experienced teacher who shows you the plants can save you weeks of frustrating efforts alone with a computer. Dokmai Dogma can never replace Dokmai Garden, it is just an addition!
Boerhavia diffusa or ‘hog-weed’ from an area with thick vegetation. The plant is easily recognized by its pairs of leaves of unequal size, their silvery undersides and the pink flowers on long stalks from the leaves. Erect or trailing, small or large, branched or unbranched flowering stalk are characters which seem to vary with the place of growth (habitat). ‘Boerhavia’ was coined by Linnaeus in honour of his Dutch colleague Hermann Boerhaave (1668-1738).
Text & Photo: Eric Danell