Pachypodium baronii, the Madagascar palm or bontaka, is a flowering plant in the family Apocynaceae.
This plant is endemic to Madagascar, where it grows in open deciduous forest on Mesozoic calcareous rock and granite or gneiss on the western side of the island at low elevations.
Pachypodium baronii is a robust, globose (spherical)- to bottle-shaped shrub in habit.
Its bark is colored pale grey or grey-green and is smooth, but sometimes retains remnants of leaf scars.
Its basal (lower) part of the branchlet is conical and laterally compressed at 0.33 to 0.66 times the spine's length.
The spines are often red and pubescent, hairy when young, turning medium to dark brown and glabrous and smooth.
The leaves are petiolate, meaning that they bear a stalk that attaches to the stem and to the leaf blade.
When dried, the blade is papery, ovate to obovate or narrowly so, and 1.4 to 3 times as long as it is wide.
The secondary veins are in 15 to 30 pairs, straight, upcurved at the apex, and forming an angle of 45–90° with the costa--the rib, ridge, or especially the mid-rib, for instance, of a leaf.
The inflorescence of Pachypodium baronii is pedunculate, having a main axis to flower stalk.
The bracts are longer than the sepals and are pubescent, hairy outside, glabrous, smooth, without hairs inside.
In P. baronii's case, the sepals are dark green, connate at the base for about 0.2 mm (.008 (0.098-inch), persistent until maturity of the flower, and ovate or narrowly so.
At the apex, the bud is acuminate, tapering gradually to a sharp point, to obtuse, having a blunt or rounded tip.
The stamen is the male reproductive organ of a flower where it usually has a filament and, at least, an anther.
The pistil is the female reproductive organ of a flower that is composed of an ovary and several free carpels the style and the stigma.
It is pubescent on the part not covered by the disk, a disk-like structure that secretes nectar.
In P. baronii, the disk is composed of five unequal glands, where 2 or 2 pairs are fused partly or entirely.
The fruit of Pachypodium baronii is made up of 2 separate mericarps, the part of the ovary or carpel that has one or more enclosed seeds.
It is rounded at the apex, obtuse at the base, and has a margin that is revolute towards the hilar side.
"metamorphic basement" means a geological complex of undifferentiated igneous and metamorphic rocks where the rocks themselves have altered their composition, texture, or internal structure through extreme heat, pressure, and the introduction of a chemical.
These steep rocks are often located in low open dry, xeric deciduous western forests where they take advantage of micro-environments suitable for succulents.
Other vegetative types, often site indicators of micro-environments, are associated with P. baronii in habitats, such as Pachypodium sofiense Apocynaceae, Uncarina sp., (Pedialaceae) Aloe bulbillifera (Asphodelaceae), Euphorbia milii (Euphorbaceae), Kalanchoe gastonis-bonieri (Crassulaceae), and Urera sp.
The substrate for Pachypodium baronii in cultivation is an acidic loose peat mixed with gneiss sand at a pH level of 4.
The Harvard University Herbaria does; however, list each botanist separately so that it is easy to discern their identities.
Again Harvard University Herbaria does not list "Constantin & Bois" as a team who worked together.
Its Species Type: Madagascar, Antsiranana, Upper Sofia R., Antsakabary, Perrier de la Bâthie 15082 (holotype P).
Rapanarivo et al. and apparently others have considered it a synonym for Pachypodium baronii.