Opuntiads of the USA

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Opuntia austrina Small 1903

Introduction

Opuntia austrina is a different-appearing cactus from the Southeast.  It can be appealing when it stands up and makes a small bush, especially when in flower or with ripe fruit.  Plants typically have a well defined trunk.  They may grow in disturbed areas (e.g., cow pastures) or in undisturbed areas (see below, article by D.A. Green). Photos copyright D.A. Green, 2006, 2007, and 2008.

Technical Description

Nomenclature:  O. austrina has been identified and misidentified over the years and given a variety of names.  The following names have, apparently, been used to designate the species at one time or another:  O. cumulicola, O. youngi, O. polycarpa, O. youngii, O. humifusa var. austrina, O. compressa var. austrina, and O. pollardi.

Subshrubs: with limited branching, generally held above the ground at intervals or entirely, sometimes a rambler and sometimes with a multitrunked tree-like shape. 

Cladodes:  narrowly or broadly obovate, 2-5(6) inches long, color variable from jade green to mahogany, not easily detached, cladodes are variable and may range from terete, oval, and most commonly obovate. 

Glochids:  tan or pale-yellow, numerous, tufted, at most areoles

Spines: Off white or gray with age, 1/2 inch, can be longer, on many areoles especially distal portion of cladode or edges, typically 0 or 1 per areole.  

Flowers: surrounded by prominent, fleshy leaves in bud, tepals yellow,

Fruits: 20 to 40 mm long, 12-20 mm wide, cylindrical or barrel-shaped with prominent narrowing at base, umbilicus present, ripening to rich dull-red with mature. 

Roots:  tuberous, nothing else with similar roots in Florida area. 

Opuntia austrina, with fruit, Florida

Close-up of plant at left

Cultivated Opuntia austrina in bloom

An article contributed by Daniel A. Green, Photographs and Text © November, 2005.

Opuntia austrina is a species endemic to the coastal plains of the southeastern United States, Florida being the state that it is most commonly found in. Opuntia austrina is considered a sub shrub that can be seen in habitats such as cow pastures, pine palmetto flat woods, and in higher areas of the scrub in close proximity of Sand Pine (Pinus clausa) and Florida Rosemary (Ceratiola ericoides). Opuntia austrina can have a well defined trunk with the plant reaching a height of a meter or so. However you would usually see Opuntia austrina grow up to half of that on average.

The species that the Opuntia austrina is commonly confused with is Opuntia humifusa. The differences are as follows:

• Opuntia austrina has tuberous roots, the Opuntia humifusa has sparse fibrous roots
• Opuntia austrina generally has an upright growth habit whereas Opuntia humifusa is very low to the ground (hence the specific epithet “humifusa”. Sometimes you may see it grow up to around 30 cm high at the most but usually it’s much less.
• The leaves on the newly forming cladodes of Opuntia austrina are perpendicular to the surface of the plant; the leaves on the Opuntia humifusa are parallel to the surface of the cladode.
• The flower buds on the Opuntia humifusa tend to be more elongated than the Opuntia austrina.
• The cladodes on the Opuntia humifusa are generally more oval and somewhat thick plus the fact that it detaches very easily is a trait common to Opuntia humifusa. Opuntia austrina has cladodes that are narrowly or broadly obovate and there are times that I have found terete cladodes on this species.
• Seedling morphology between the two species differs as well.  

Opuntia austrina, 5/2003, State Road 434, Orange County FL, with elongate cladodes

Opuntia austrina with a flower bud, University of Central Flrodia, May, 2003, with turkey oak (Quercus laevis).

Opuntia austrina with leaves on the cladodes.

Opuntia austrina in fruit, near University of Central Florida.

Opuntia austrina, University of Central Florida campus, May, 2003.