Shape and size adjustments of a cactus with rib and furrow morphology

- Cactus have accordion-like form for water storage, thermal, photosynthesis benefits.
- S- and morning sun E-facing ribs are more closely spaced gaining photosynthetically.
- Furrow size relates to long-term adjustments with growth for conditions.
- Intraspecific crowding and shade affect furrow size.
- adaptations for short (ribs) and long-term (furrows) adjustments for environment.

Hundreds of cactus species have evolved the rib and furrow morphology that aids in water storage and provides photosynthetic and thermal benefits. Limited work has been done on understanding rib spacing and furrow size in the context of a wide range of environmental variables. Data were collected in two Carnegiea gigantea Sonoran Desert (Northern Hemisphere) populations, that were analyzed using General Linear Models and MANOVA to assess the relationships between rib and furrow metrics, height and direction on the plants, and several environmental and plant-wide variables (e.g., intraspecific crowding, shade, branching). Furrow sides are smaller lower on the plant, but are not related to orientation suggesting adjustment with growth. Rib spacing is not related to height on the plant, but is related to direction (greater spacing to the north and west), likely due to thermal and photosynthetic differences. Intraspecific crowding and shade affect the size of furrows. This morphology offers both a long-term response to general conditions (furrow size, e.g., shade, regional factors) and short-term response (rib spacing) to seasonal variations in temperature and moisture for direct response to fluctuating conditions. These mechanisms will continue to be important with changing climate, and through range shifts associated with warming.