Excerpts from Jim Conrad's
from the April 20, 2014 Newsletter issued from the Frio Canyon Nature Education
Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau, USA
LITTLE NIPPLE CACTUS
Neighbor Phred had told me that in the local cobblestone fields of the floodplain of the little Dry Frio River there used to be little cacti shaped like bunches of green jalapeño peppers joined at their stems. With their rounded bottoms pointing outward, each bottom was equipped with numerous stiff spines. Cactus connoisseurs will recognize that we're referring to a kind of nipple cactus of the genus Mammillaria.
So far I'd not seen any Mammillarias, and I'd figured that local people had dug them all up for potting, or maybe the occasional attempts to exterminate our Ashe Junipers had squashed or burnt them all. However, this week a small cluster turned up on the cobblestone floodplain, shown above.
The population was about the size of a saucer. In the picture there's an older body on the right, a younger one at the left, and quite young ones emerging with pale spines in the center, below and above. A close-up of the spines atop a "nipple" appears below:
In that picture, notice that each spine cluster consists of a single thick-based spine emerging from the center of a cottony zone at the nipples top, surrounded by about a dozen smaller, outward-radiating spines.
Mammillaria is an important cactus genus, containing about 164 species, all restricted to Mexico, Central America, the West Indies and the southwestern US. The Flora of North America describes 14 species in the US. Important field marks leading us to the identity of this one include the following:
Books call this the Little Nipple Cactus. It's MAMMILLARIA HEYDERI. It's the most widely spread Mammillaria species in the US Southwest, occurring from southern Arizona and New Mexico through western and southern Texas, plus the arid northern half of Mexico. On the Internet it's mainly documented as a potted plant. When they're potted and taken care of they grow larger than ours, with many more "nipples," and more regularly spaced spine clusters. Gardeners consider Little Nipple Cactuses as one of the most cold-hardy of Mammillaria species.