Pachypodium brevicaule. Low growth form and yellow flowers
The low, expanded stem of Pachypodium brevicaule with leaves and yellow flowers.
Illustrative depiction supplied by the site author.
Enlarge plate ↗Caudex and compact shoots
Lüthy describes a caudex that is usually broader than tall and bears numerous apices. Extremely compressed shoot segments arise from these growing points. Spines on young growth are soon shed, and leaves cluster at the shoot tips. The habit results from the crowding and shortening of axes that form elongated branches in taller members of the genus. [Lüthy 2004]
Flowers, fruits and subspecies
The flowers have a cylindrical upper corolla tube. Compared with Pachypodium rosulatum, the sepals are broader and the inflorescences and fruits more distinctly pubescent. Inflorescence stalk length varies. At exposed sites described in the revision, the stalks could be so short that flowers appeared close to the caudex surface. The seeds examined in that revision were small and smooth. [Lüthy 2004]
POWO recognizes two subspecies, Pachypodium brevicaule subsp. brevicaule and Pachypodium brevicaule subsp. leucoxanthum. Burge and colleagues list yellow flowers for the nominal subspecies and white flowers for subsp. leucoxanthum. The species in its broad sense therefore includes more than one corolla colour. [2-WWW] [Burge et al. 2013]
Upland habitats
Lüthy’s revision records habitats at 1250–2200 m in central Madagascar, a range compiled from earlier field observations. Elevation helps distinguish its environment from the lowland habitats of many tree-form Pachypodium species. [Lüthy 2004]
Photosynthesis and relationships
Eder and colleagues classified the tested Pachypodium brevicaule as C3 plants. Their isotope table gives δ¹³C values of −28.52‰ for the stem and −29.67‰ for the leaves. The paper uses the species name without a subspecific identification. The modern subspecies classification is kept separate from the identification used in that experiment. [Eder et al. 1981]
In the 2013 phylogeny, Pachypodium brevicaule samples belonged to the Malagasy section Gymnopus. Samples of the broadly circumscribed species did not form a single exclusive lineage in the reconstructed tree. The authors considered hybridization and retention of ancestral genetic variation as possible explanations for such patterns in this group. This interpretation rests on the two DNA regions examined. [Burge et al. 2013]
Own-root and grafted plants
The 2004 account records grafting Pachypodium brevicaule onto Pachypodium lamerei. The way a specimen is maintained is therefore part of its horticultural description. In a grafted plant, the root system and lower stem belong to the rootstock, while the characteristic low caudex belongs to the scion. This information helps interpret the appearance and history of an individual specimen. [Lüthy 2004]
Related articles
Materials from the author's archive
The species also appears in Konrad Szychowski's private material archive. [Neciu 2005]