All Pachypodium are succulent plants that exhibit, to varying degrees, the morphological characteristics of pachycaul trunks and spinescence.

Variation in habit can range from dwarf flattened plants to bottle shaped shrubs to dendroid-shaped trees.

For example, Pachypodium can sometimes occur in prehumid vegetative zones where a taxon might find a suitable habitat on a rocky, sunny inselberg jutting above the humid canopy of the forest.

Freeform branching is a morphological adaptation to factors of the immediate microenvironment which, by their diversity, account for the wide range of habits: Despite microenvironmental variation, Pachypodium are always succulent and always exhibit pachycaul trunks.

In addition to the lower surface-to-volume ratio which aides in water retention, the thickened trunks and branches can also possess photosynthetic surface tissue to allow nutrient synthesis even when leaves are not present.

Fog condenses on their spines in the form of dew, which drips down to the ground and increases the amount of moisture that's available to their often shallow roots.

Three factors can be seen to attribute speciation, or the occurrence of species diversity, via adaptive mechanisms to accelerated evolution as it occurs within the xeric landscape and climate.

(1) The variation of geology and topology in dry climates is thought to have a greater effect upon plants than in areas with high rainfall.

(3) Taxa tend to develop specialized xeromorphoric structures at some architectural level in arid, geological and topological landscapes, where a strategy of a "flexible" and "strict" architectural, organizational morphology at various levels of structure for Pachypodium becomes advantageous to succeeding in the isolated, specialized landscape.

This strategy is seen in the manifest flexible variations of habit in species of Pachypodium while all the same they are "strictly" xeromorphic pachycaul trunks meant to conserve water for dry periods.

For instance, there is an advantage to morphologically developing into bottle-shaped "shrubs" where the plants exist in open, sunny microenvironments on top of porous sandstone.

Likewise, where competition for resources is more competitive—both in the number of species and the height of surrounding plants—there are times when it is to the advantage of a plant to develop into arborescent, dendroid "trees."

This development is because these particular Pachypodium must compete with other plants for resources in a dry deciduous forest, composed of, perhaps, arborescent Aloe, members of the Didiereaceae genera Alluaudia, Alluaudiopsis, Decaryia, and Didierea (all endemic to Madagascar), and Uncarina species, for instance.

The adaptive mechanism in a morphological form and an ecological response to habitats are typically manifested together at once for the genus Pachypodium.

The genus' unique organizational, architectural morphology shapes plants that are highly, adaptively responsive to their immediate, surrounding, microenvironments.

The duplicity of an adaptive mechanism that is at once "strict" and "flexible" at differing levels of plant physiology, or structure, has granted Pachypodium the ability to evolve within the landscape into variations that fulfill an ecological niche as various species.

The development of new species is through, in part, the adaptive mechanisms of pachycaul and spinescence as well as strict and flexible structural organization at various levels of plant physiology.

The family Apocynaceae before it included Asclepiadaceae had 3 genera that can be considered succulent plants: Adenium, Pachypodium, and Plumeria.

A precipitation regime for a species of Pachypodium, therefore, depends upon a habitat's location relative to the influences of the Atlantic and Indian Oceans and the various mountain ranges of southern continental Africa and of Madagascar.

On outcrops, steep hills, and inselbergs, the plants are subjected to fluctuating moisture, high winds, and temperature extremes.

This saturation of crevices can only occur, however, if there is not a considerable runoff from the rock's surface and if there is abundant fine soil in the cracks that, in turn, retain water.

Where water is in deep sandy substrate, Pachypodium grow on sand "over" laterite red soil.

The protection afforded by the CITES treaty responses to two issues: Extinction of identified species seems yet unlikely, as the collection of seed and the cultivation of the plant safeguard the genus.

In 1907, Costantin and Bois constructed the first monograph, of Pachypodium, in which they enumerated 17 species, where ten were from Madagascar and seven were from continental southern Africa.