Opuntia retrorsa

Name and distribution

The accepted name is Opuntia retrorsa Speg. (formerly also O. anacantha var. retrorsa, and O. viridirubra in the pollination study). POWO gives a range covering Bolivia, Brazil, Paraguay, Uruguay and northern Argentina. The results described below come from a southern Brazilian population identified in the study as O. viridirubra. [2-WWW] [Schlindwein and Wittmann 1997]

Structure of plants from Guaritas

In the Guaritas region, shrubs reaching about 1 m tall were observed, with rounded buds and orange or yellow flowers. The flower including the ovary was 65–85 mm long and 59–72 mm wide, and the stigma had 9–10 lobes. Plants occupied sunny rock outcrops and shallow soils in a mosaic of grasses and shrubs. [Schlindwein and Wittmann 1997]

Flowering and stamens

Flowering was observed from late October to February. An individual flower remained active for a total of 6–12 hours. Mechanical stimulation caused the stamens to move towards the pistil, with their return towards the initial position taking a dozen or so minutes. The strongest response occurred early in the flower’s life. [Schlindwein and Wittmann 1997]

Bees and access to pollen

30 bee species were recorded in flowers of this taxon. Pollination effectiveness was assessed from stigma contacts, pollen load composition and flight routes. Females collecting opuntia pollen were particularly important, reaching the interior of the stamen arrangement and moving between plants. [Schlindwein and Wittmann 1997]

Hand self-pollination confirmed that seeds could be set with the flower’s own pollen. Flowers isolated without hand pollination produced very few seeds, while cross-pollination gave results similar to flowers accessible to bees. The study therefore links the flower’s movement response with pollinator behaviour and the final reproductive outcome. [Schlindwein and Wittmann 1997]