Cacti on the branches of dry shrubland

An inventory above and on the ground

Aguilar-Cruz and colleagues conducted an inventory in July 2023 at three sites in the Mexican reserve. They found approximately 1400 cacti over about a quarter of a hectare. They recorded species, dimensions, flowers or fruits, and growth location. Epiphytism, growth on another plant without roots reaching the soil, occurred in at least nine of the thirteen locally recorded species. [Aguilar-Cruz et al. 2026]

Globose plants and young candelabra cacti

For the six most abundant groups, the figure records 680 epiphytic and 689 terrestrial individuals. Their distribution differed markedly among species. Mammillaria polythele and M. crinita occurred mainly on trees, whereas M. longimamma was predominantly terrestrial. Myrtillocactus geometrizans and Isolatocereus dumortieri also grew epiphytically, but their small individuals dominated on branches. [Aguilar-Cruz et al. 2026]

Some tree-growing M. polythele and M. crinita bore flowers or fruits. In both arborescent species, the largest plants occurred mainly on the ground. The observations therefore suggest different capacities to complete the life cycle in this microhabitat. The fate of small cacti on branches requires further demographic monitoring. [Aguilar-Cruz et al. 2026]

Neltuma as the principal host

Approximately 99% of epiphytic cacti grew on Neltuma laevigata. The two remaining cases were Mammillaria polythele on large Isolatocereus dumortieri. Within Neltuma crowns, cacti often occupied relatively thick, nearly horizontal branches. The authors observed a thin layer of material derived from decomposing bark, lichens and leaves beneath them. [Aguilar-Cruz et al. 2026]

Larger crowns were associated with more cacti. They may provide larger seed-trapping surfaces and more diverse microhabitats. The authors also consider buffering of extreme conditions and longer moisture retention in accumulated substrate. These are proposed mechanisms explaining the distribution and require direct measurements within the crowns. [Aguilar-Cruz et al. 2026]

Size changes the conditions of life

A small seedling requires a different amount of substrate and space from a cactus several metres tall. Growth also increases the load on the host branch and the effects of wind. The authors identify spatial and mechanical constraints as possible explanations for the contrast between young epiphytic I. dumortieri and large terrestrial plants. The inventory represents one area and sampling period. Within that scope, it shows that a species’ habitat can include several forms of establishment. [Aguilar-Cruz et al. 2026]