Botany of Madagascar

Of the world's baobab species, six are endemic to Madagascar, one is widespread in mainland Africa, and one occurs in northwestern Australia. That distribution is one of the classic puzzles in plant biogeography, and recent phylogenetic and genomic work has placed the origin of the genus on Madagascar with subsequent oceanic dispersal outward, a conclusion that inverts the older assumption.

In the field, participants measure and compare Adansonia grandidieri, A. za, A. rubrostipa and others where ranges permit, recording trunk form, bark texture, flower structure and phenology. The pollination story differs by species, hawkmoths for some, lemurs and fruit bats for others, and provides an immediate lesson in coevolution.

Regeneration is the pressing applied question. Many famous baobab stands are ageing populations with almost no recruitment, because the surrounding land is now agricultural and seedlings do not survive. Participants collect stand-structure data that speaks directly to that problem.

The spiny thicket of the southwest is dominated by the Didiereaceae, an almost entirely endemic family whose members look convincingly like cacti, succulent, spined and water-storing, but are unrelated to them. It is the cleanest field demonstration of convergent evolution available anywhere, and it can be seen from a single vantage point.

Participants study the anatomical basis of that convergence: water-storage tissue, reduced or deciduous leaves, photosynthetic stems, CAM and CAM-like metabolism, root architecture. They also study the endemic Pachypodium, Alluaudia and Euphorbia forms alongside them, and the extraordinary reality that lemurs move vertically through a forest of spines.

The spiny forest is also under severe pressure from charcoal production and clearance for maize, so vegetation plots here double as a monitoring exercise with real conservation relevance.

The methodological backbone of the course is proper botanical practice. Participants learn to press and dry specimens correctly in humid conditions, take complete collection data, record features lost on drying, produce a legible field description, and prepare duplicate sets for deposition with Malagasy partner herbaria.

Alongside collecting, they run quantitative vegetation work: nested quadrats, point-centred quarter sampling, diameter-at-breast-height inventories, canopy cover estimation with densiometers, and phenological transects recording flowering and fruiting. They construct species accumulation curves and see for themselves why tropical inventory effort is never complete.

Identification is taught through the reality of an incompletely keyed flora, using generic characters, comparison with reference material, and the honest recording of an unresolved determination rather than a confident guess.

Madagascar's plants are also a livelihood and a market. Vanilla, the world's second most expensive spice, is grown here in a Vanilla planifolia system that is hand-pollinated because the natural pollinator is absent, an ethnobotanical and economic story in itself, with real consequences for forest communities in the northeast.

The Madagascar periwinkle, Catharanthus roseus, yielded vincristine and vinblastine, transforming treatment of childhood leukaemia and Hodgkin lymphoma. That single example anchors the entire discussion of bioprospecting, benefit sharing and who owns the value derived from a national flora.

The orchid flora, around a thousand species and mostly endemic, connects to illegal collection and CITES enforcement. Participants meet nursery and enforcement staff and see the practical mechanics of plant trade regulation, then work in community reforestation nurseries where native species propagation is the actual daily labour of conservation.