In addition to the flower, today’s photo also shows the needle-like stinging hairs that give this species its common name, desert stingbush.
Eucnide urens is a small rounded bush that grows in well-drained soils from California to southwestern Utah and Arizona (and south into northern Mexico). Most parts of desert stingbush, including stems, buds, and leaves are covered by barbed spines that release an irritating toxin when bumped or brushed. When green, these spines cling to soft surfaces, much in the way that Velcro® sticks together. If the spines are dry when touched, they are very painful and difficult to remove. This is a characteristic of many species in Eucnide, which in Greek means good (eu) stinging nettle (knide).
Unlike the rest of the plant, desert stingbush flowers are not covered with spines. The flowers are a favoured food of the bighorn sheep (Ovis canadensis), who must still have to eat these delicate flowers carefully! The flowers are large (5cm across), white to cream, and have five petals. Eucnide urens blooms profusely, with mature bushes containing hundreds of flowers that are sometimes so plentiful that the leaves cannot be seen below them.
Eucnide urens is labeled in this article by the International Carnivorous Plant Society as a “murderous plant”. That’s right – not a carnivorous plant, but a murderous one. According to this article, the toxins released by the spines kill syrphid flies that come into contact with them. Without a mechanism for consuming these flies, Eucnide urens leaves amass a graveyard of syrphid fly (Syrphidae spp.) carcasses. The flies are attracted to aphids that feast on desert stingbush (the aphids are somehow unaffected by the spines). It seems unfortunate for Eucnide urens that its spines protect a pest species from its predator. I was not able to find any primary research that addressed the adaptive roles of desert stingbush’s spines, but presumably whichever consumer the spines do protect against causes more damage than aphids can.