Excerpts from Jim Conrad's
Naturalist Newsletter


from the the September 9, 2012 Newsletter issued from the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA

On a rocky ledge over the Dry Frio River right behind the cabin several pricklypear cacti are now adorned with egg-shaped, egg-sized fruits, or tunas, as shown above.

In general, cactus taxonomy is a mess, maybe because few taxonomists want to work with such spiny, hard-to collect plants as cacti. In the Cactus Family, the Cactaceae, one of the biggest and most easy-to-recognize kinds of cactus is the pricklypear group, genus Opuntia. The cactus in our picture is a pricklypear, a fairly representative one with its beavertail-shaped pads (modified stem segments) arising from one another. But which of the 34 or so North American pricklypear species is it?

Important field marks to notice for this species include that the plant is sprawling instead of rising on a sturdy trunk, and that the pads are fairly large and broad, sometimes almost circular. The pads are dull green, not a lustrous, deep green. The groups of spines are relatively widely spaced across the pads' faces, and the spines themselves are pale yellowish, not grayish, and tend to point downwards. Other important field marks are shown in a close-up of one of the little bumps, or areoles, from which spines, leaves and other structures arise, below:

Texas Pricklypear, OPUNTIA ENGELMANNII var. LINDHEIMERI, close-up of glochids and spine bases

There you see that the large spines are flattish at their bases, and only slightly reddish instead of dark red. The numerous small spines at the base, called glochids, cluster on one side of the areole and, for glochids, are unusually large. These are important matters in pricklypear identification!

Keying our cactus out in the online Flora of North America leads to the name OPUNTIA ENGELMANNII var. LINDHEIMERI, often known as the Texas Pricklypear. This variety, lindheimeri, is typical of the Chihuahuan Desert of northern Mexico and southern Texas. The broader species is found from southern California north to Utah, east through southern Texas, and south through much of arid northern Mexico. Also, the broader Opuntia engelmannii is one of the most taxonomically difficult and tossed-about of all pricklypear species. Each of my three cactus field guides uses a different binomial name for it.

Del Weniger, author of Cacti of Texas and Neighboring States -- a book that delighted me while backpacking in Big Bend National Park a few years ago -- is a real cactus lover, yet on his page for the Texas Pricklypear uncharitably he refers to this lindheimerii variety of Opuntia engelmannii as the "worst pest pear of south Texas." I personally have always been pleased to meet it, however, and find nothing pestiferous about it. I think he is trying to say that the species is uncommonly flexible in its habitat requirements, and is capable of surviving in many places humans disturb.

from the April 28, 2013 Newsletter issued from the Frio Canyon Nature Education Center in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA

I've been waiting for the pricklypears to begin flowering, and now they have, as you can see below:

Texas Pricklypear, Opuntia engelmannii var. lindheimeri, flowering

Below you see a close-up of how the rose-like, rose-tinted flowers cluster atop the pads:

Texas Pricklypear, Opuntia engelmannii var. lindheimeri, flowers

A view inside a blossom showing it colonized by beetles, and from its center arising a thick, pink style with a large, yellow, oval stigma atop it is shown below:

Texas Pricklypear, Opuntia engelmannii var. lindheimeri, interior of flower showing greenish stigma

Noting these colors was useful because they vary from species to species. Spine color, number and configuration of the confined area they arise from -- their "areoles" -- also is important, so they are shown below:

Opuntia engelmannii areoles

Already we've identified the abundant cactus on the valley floor and surrounding hills' lower slopes as the Texas Pricklypear, Opuntia engelmannii var. lindheimeri. Since the ones on the valley floor haven't begun flowering yet and the individual pictured above was near the crest of a limestone hill, I had hopes that this would a new species for us.

However, using the key to pricklypears available online in the Flora of North America, of the 34 pricklypear species known to occur in the US, the key led me directly to our plentiful Texas Pricklypear. You can try your own hand at IDing the flowering cactus shown in our photos at http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=123045.

I still have hopes of finding other pricklypear species here, but I won't be able to identify them until they flower.

from the June 16, 2013 Newsletter issued from the Frio Canyon Nature Education Center in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA

In very thin, dry soil exactly at the lip of a limestone cliff dropping to the little Dry Frio River behind the cabin a couple of cylindrical, four-inch tall (10cm) cactuses showed up, one of which is shown below:

Pricklypear seedling

A close-up of the cactus's clusters of spines appears below:

PRICKLYPEAR CACTUS SEEDLING close-up showing spine cluster

In our area we have cylindrical cactus species bearing clusters of numerous slender spines radiating from a point, as shown above, but I've not seen them in the wild, despite our being in their area of natural distribution. You see them in people's yards, and I'm guessing that basically that species has gone extinct in this area because of people digging them up.

However, even mature pricklypear cactuses with flat, beavertail-shaped stem segments, or pads, start out as cylindrical seedlings, and that's what I think is shown in the picture. Since several large, prolifically fruiting Texas Pricklypears, Opuntia engelmannii var. lindheimeri, were growing just a few feet away, so I'm supposing that that's what is shown in the picture.

In the last picture notice toward the cactus body's top, in each spine cluster a single spine is pinkish and more robust than the surrounding paler and much smaller spines. Mature spine clusters of the Texas Pricklypear normally develop only one or two large spines per cluster.