Excerpts from Jim Conrad's
from the March 15, 2015 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
GAUMER'S NOPAL CACTUS
In this year's January 4th Newsletter we looked at a 4.5m tall (15ft), prickly-pear-type cactus, the Scrub Cactus, Nopalea inaperta, common in this area. Our Scrub Cactus Page is at http://www.backyardnature.net/yucatan/inaperta.htm.
On that page I mention that another very similar cactus shares the same limited distribution with the Scrub Cactus, and that's Gaumer's Nopal Cactus, Nopalea gaumeri. Some specialists say that Gaumer's Nopal Cactus is a mere variation of the Scrub Cactus, while others list it as a distinct species. Since publishing the Scrub Cactus Page I've been waiting to find cacti answering to the description of Gaumer's Nopal Cactus, to see what I thought about the situation. Now I've found some, and they were flowering. The plants were much smaller than Scrub Cactus, only about knee high, as shown above.
As with the earlier Scrub Cactuses, these plants grew amidst thick brush in thin soil atop limestone. In fact, numerous Scrub Cactus plants inhabited the same area. A 2m tall one (7ft) stood only 3m away (10ft) from the small one in the picture. Several of these smaller cacti were in the area, but also there were cacti of intermediate size. The smaller cactus's joints were less flattened than those of the bigger ones, but there were transition states between cylindrical and flattened, too. So, just focusing on cactus size and joint shape, it was hard to say whether two species were being dealt with, or just one.
However, one big difference between the tall and short plants was that all the smaller ones were flowering, while the larger Scrub Cactuses mostly were not. A branch showing some of the short cactus's spiny pads and flowers is shown below:
A close-up of a flower showing the yellow-green, deeply lobed stigma on its white style protruding beyond a dense cluster of stamens with yellow anthers and pink filaments is shown below:
Another feature the above picture shows is that the green ovary below the red sepals and corolla bears clusters of well formed spines. The larger Scrub Cactus's ovaries also bear spine clusters, but the spines are shorter and more slender than these.
A look at spine clusters on the small cactus's pad is seen below:
So, do I think that these small cacti constitute the distinct species known as Nopalea gaueri, or are they just a local variation of the common Scrub Cactus, Nopalea inaperta?
On the basis of the smaller cactuses all flowering at the same time while surrounding Nopalea inaperta plants were only rarely flowering, and because of the much larger spines on the smaller cactus's ovaries, I'm thinking that probably two species are involved, and that the smaller ones are NOPALEA GAUMERI. This species really has no English name, but we'll call it Gaumer's Nopal Cactus.
Gaumer's Nopal Cactus is endemic to only the northern third or so of the Yucatan Peninsula, and mostly in the more arid northwest.