Plant of the Week
Plateau Yellow Miner’s Candle (Cryptantha flava)
By Walter Fertig
Western North America is home to over 100 species in the genus Cryptantha of the borage family (Boraginaceae). Commonly known as cryptanths, cats-eyes, or miner’s candles, Cryptantha species vary considerably in growth form (annual, biennial, or perennial), flower size, leaf and stem pubescence, and fruit characteristics. The group has a reputation for being difficult to identify, although most species can be distinguished on the basis of unique fruit morphology. Nearly all cryptanths have white flowers, but a few, like Cryptantha flava, have opted for yellow blossoms instead. Not surprisingly, flava is Latin for yellow.
Plateau yellow miner’s candle is a perennial with an elongate, bristly inflorescence subdivided into 5-10 ball-like flower clusters of approximately equal size. The individual flowers have five petals fused into a slender tube that extends beyond the sharp-bristly calyx. In C. flava, the flowers come in two forms: pin flowers in which the styles exceed the anthers and reach the rim of the corolla tube and thrum flowers where the styles are shorter than the anthers and completely contained within the floral tube. Having two flower types helps promote cross-pollination, as insect visitors to different flowers will pick up (and deposit) loads of sticky pollen on different parts of their body depending on whether they have visited pin or thrum blossoms.
This isn’t the only reproductive trick up the plant’s sleeve. Most cryptanths produce four hardened, one-seeded, nut-like fruits (called nutlets) per flower. In Plateau yellow miner’s candle, only one (or rarely two) of the incipient nutlets survives to maturity. Producing ¼ the number of seeds potentially available would seem to be a disadvantage, but researcher Brenda Casper has found that producing fewer fruits allows C. flava to invest more energy into the surviving seed and that this single seed can be dispersed within its bristly calyx (conferring greater protection from seed-eating rodents), rather than as a naked fruit like its four-seeded relatives. Casper has found that all four nutlets have the potentially to ripen, but that competition among them results in only the largest one or two surviving.
Cryptantha flava is relatively common in sandy desert areas from southern Wyoming and eastern Utah to northern Arizona and New Mexico. Over much of its range it co-occurs with another yellow species, Basin yellow miner’s candle (C. confertiflora). The latter can be distinguished by its denser inflorescence with one main, terminal clump of flowers and a few smaller ones and by producing the standard four nutlets per flower. These nutlets also tend to be shorter and wider than those of C. flava.