Pachycauls

Pachycauls are plants defined by having thick, fleshy stems that are large in diameter relative to their height. The term comes from Greek roots meaning thick stem. It is a descriptive growth form rather than a strict taxonomic group, and it can occur across several plant families.

Morphology and characteristics include a substantial trunk or caudex that stores water and nutrients, with relatively few branches. Leaves, if present, are often reduced or deciduous, and the growth habit can range from bottle-shaped to columnar or irregular forms. Many pachycauls retain their thick trunk for many years, with foliage concentrated near the apex in favorable conditions.

Distribution and ecology: Pachycaul forms are common in tropical and subtropical regions and in arid or seasonally dry environments. The water-storage capacity of their trunk helps tolerate drought and irregular rainfall. While many are succulent, others are more tree-like in appearance, and some may flower or fruit from the upper crown.

Taxonomy and examples: Because pachycaul is a growth form rather than a lineage, it spans multiple genera. Notable examples include various euphorbs and caudiciforms such as Euphorbia species, Pachypodium species, and Adenium species, as well as large arborescent trees like baobabs (Adansonia). The presence of a pachycaul form does not imply close relatedness among species; it describes morphology shaped by ecological pressures.

Cultivation: In horticulture, pachycauls are prized for sculptural trunks. They generally require bright light, well-drained soil, and staged watering to avoid rot, with a pronounced dry period recommended for many species. Repotting should be done carefully to protect the thick stems.