Stem and flower structure
In the nominal subspecies, branches often arise near the base. They may be ascending, arching or lax. Leaves cluster at their tips, and the spines occur in pairs. The fused petals form a tube with a narrow, nearly cylindrical upper part. The ovary is pubescent, a character shared with other members of section Gymnopus. [Lüthy 2004]
Lüthy compared flowers approximately 6 cm across in subsp. rosulatum with flowers around 3 cm across in subsp. gracilius. The latter develops a pronounced, rounded caudex and shorter, ascending branches. Subsp. cactipes has more regularly and widely spaced needle-like spines. These comparisons apply to particular subspecies and help describe plants of known provenance. [Lüthy 2004]
Subspecies and historical names
POWO treats Pachypodium gracilius as a synonym of Pachypodium rosulatum subsp. gracilius. Pachypodium cactipes corresponds to subsp. cactipes. Pachypodium drakei is included under the nominal subsp. rosulatum. This treatment connects older labels and publications with the relevant part of the species. [2-WWW] [2-WWW] [2-WWW]
Habitats and leaf retention
The nominal subspecies includes plants from northwestern and north central Madagascar. Lüthy discusses both exposed-rock plants with shallow substrate and plants historically called Pachypodium drakei from more shaded sites with deeper, sandy soil. Their characters were also compared in cultivation. Variation in habit is therefore considered together with the provenance of the material. [2-WWW] [Lüthy 2004]
Subsp. cactipes comes from southeastern Madagascar, around Fort Dauphin. Lüthy associates it with a relatively cool and less arid climate. He also records winter leaf retention in cultivation when some moisture is available. This observation concerns subsp. cactipes and is relevant when comparing seasonal behaviour among forms of Pachypodium rosulatum. [Lüthy 2004]
Fruits and identification of material
Fruits in the Pachypodium rosulatum group have long, slender, usually upright follicles. Their surface is glabrous or nearly so. Compared with the more strongly pubescent fruits of Pachypodium brevicaule and the thicker follicles of some other species, this character helps assess mature plants. Identification combines it with calyx, corolla-tube and spine characters. [Lüthy 2004]
Evidence from DNA
In the study by Burge and colleagues, five samples of the nominal subspecies formed a well-supported group. Taken together, however, the Pachypodium rosulatum subspecies did not form a single exclusive branch in the ITS and trnL-F tree. Some material grouped closer to other low-growing species in section Gymnopus. This result documents complex relationships within the group as resolved by the markers used. [Burge et al. 2013]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Neciu 2005]