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Nylon hedgehog cacti have flowers on stems emerging from their sides. (Jeff Mitton / For the Camera)
Nylon hedgehog cacti have flowers on stems emerging from their sides. (Jeff Mitton / For the Camera)

While walking along the Coalton Trail through Boulder County Open Space I noticed some small cacti in flower. They were less than 3 inches tall and had cylindrical stemsthat were partially buried in the soil. Their spines emanated from dimples (technically, areoles) on ridges running  the length of the stems. This population had blooms that were light yellow to greenish-yellow, on stems that grew from the sides. These were nylon hedgehog cacti, Echinocereus viridiflorus.

The cactus family is all American, or almost so. Cacti first appeared in South America, perhaps associated with an uplift in the Andes. They moved north and diversified so their extant number of species is 1,400, and their highest diversity is in southern Mexico.

Jeff Mitton. Natural Selections

It is thought that birds were responsible for establishing just a few species in Africa and Madagascar. The genus Echinocereus appeared about 4 million years ago, and today it is the third-largest cactus genus.

Areoles evolved in the cactus family. They appear as a dimple bristling with spines, but developmental biologists tell us they are abortive branch buds, and the spines are modified vestigial leaves. In addition to spines, areoles may also contain glochids, which are barbed hairs that evolved from bristles. Unlike spines, the glochids have cells at their base programmed to die when development is complete, so glochids are easily detached from the cactus when the pointed and barbed end becomes embedded in skin.

I find glochids more troublesome than spines, for the fragile hairs break easily, leaving the barbed end buried in flesh to create a fierce itching. Nylon hedgehogs have only spines, no glochids.

The literature indicates that the number of Echinocereus species is from 44 to 71 — that wide range indicates that the biologists disagree. For example, one convention recognizes four subspecies (chloranthus, correllii, cylindricus, viridiflorus) and one isolated and endangered variety, davisii. In contrast, other conventions elevate some of the subspecies and the variety to full species. This controversy is not unusual for a group of species that is currently adapting to a variety of environments.

Nylon hedgehog cacti are distributed from northern Mexico through parts of Texas, New Mexico, Colorado, Kansas, Nebraska and Wyoming to an isolated population in southwestern South Dakota — from very hot, dry to very cold, dry places. Nylon hedgehogs are one of  the most cold-tolerant species and also one of the earliest blooming cacti around Boulder.

The population along the Coalton Trail has blossoms that, when viewed in the visible light range, are greenish- yellow, but other populations might have yellow, brown, brick red or russet blossoms and some have purplish- maroon midstripes on the tepals. For example, nylon hedgehogs from Big Bend National Park have russet  blooms, inspiring some biologists to name them a different subspecies or species. When viewed with UV, flowers are either entirely UV-absorbing (all dark), or with UV-reflective on the outer third of the tepals and UV-absorbing  centers (light outer ring, dark center). The latter pattern is referred to as a target type blossom, for it directs the  pollinators to the nectar and pollen.

Insect pollinators use UV patterns to identify appropriate nectar sources and to guide them to the center of  flowers. So, it is worth noting that fragrance varies among nylon hedgehogs — some emit a distinctly lemon  fragrance, and others emit no fragrance at all. Furthermore, the hedgehogs with target UV patterns emit lemon  fragrances, while those with entirely UV-absorbing blossoms have no fragrance.

Species with large geographic ranges, particularly those that also live in a variety of habitats, often exhibit adaptation to local environments. We usually think of habitats as differing in physical components of the  environment, but they also differ in biotic components, such as the pollinator species. A single, iridescent green  halictid bee is credited with most of the pollination in nylon hedgehogs, but that was a single study. I suspect that Big Bend National Park in Texas has different pollinators than the Black Hills and Badlands in South Dakota.

To compete with other plants for the services of pollinators, nylon hedgehogs might be selected, by pollinators,  for different colors, UV patterns and fragrances from place to place. I think it would be profitable to test this  hypothesis by observing nylon hedgehog cactus pollinators in populations differing in flower color, pattern and  fragrance. It would be satisfying to understand the function of all of that variation.

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