(Ker Gawl.) Haworth Supplementum Plantarum Succulentarum. 79, 1819
Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Herbarium; Drawing (Britton and Rose, v1 1919, plate XXVIII, No. 2); Drawing (Botanical Register 1817, 3: plate 255)
Opuntia dillenii is a coastal plant of the southern Atlantic coastal states and perhaps the western coast of FL. Maybe some of the Islands were home to it in pre-Columbian times. However, the species has spread to other continents including South America, Africa, Australia, and Asia and is an invasive weed in some of these new areas. The species is often conflated with O. stricta and this may obscure its actual current distribution. Some botanists even treat O. dillenii as a variety of O. stricta, and some treatments (eg, Flora of North America) don’t even recognize it. Both plants may grow in similar habitats, but they are dissimilar. One important (but not universal) difference is that O. dillenii has pads with scalloped edges. Additionally, it is much spinier than O. stricta. O. zebrina of southern FL may be a form of O. dillenii. Various ploidies have been reported for O. dillenii but it may be hexaploid. If different ploidies exist, the variants may represent two or more taxa. See the original description.
O. dillenii may reach 5(6)-ft tall but is often much shorter. Extensive stands sometimes make impenetrable thickets. Pads are often 4 inches by 6 but may be smaller or larger. The areoles have 1 to 5(10) yellow or brown spines. Areoles are raised above the cladode surface creating a dimpled look. Scalloped and dimpled cladodes with ample spines create a distinctive appearance. Spines may be 1(2)-inches long.
One reason for its weediness may be its ability to grow in various habitats such as woodlands, grasslands, creek banks, and disturbed areas such as roadsides even though it was originally a species a coastal species. It tolerates a variety of soils and mild frosts.