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Penstemon digitalis is a perennial herb plant that is native to the United States and is mostly found growing in the wild in southeastern regions such as throughout the state of Missouri. The plant typically produces white flowers with five potentially pollen-producing stamen, one of which is sterile and has an outgrowth of small hairs which has given the plant the common name of beard tongue. Since the flowers of Penstemon digitalis resemble the digitalis plant more commonly known as foxglove, Digitalis purpurea, it can be confused with this plant, but it has no value as a heart stimulant compound like true digitalis does. Two main species for the genus Penstemon are known to grow in the wild, including the digitalis variety, which is the most common, and the rare baueri variety where the leaves have whorl patterns in groups of three.
Plants in the Penstemon genus have elongated, round-blade shaped leaves and can grow to a height of 3 to 5 feet (0.9 to 1.5 meters) in the wild. The species has become widespread throughout the south eastern region of the US and is found in prairies and many wooded or semi-wooded locations. It thrives best where the climate tends to be warm and wet, though it can appear as far north as hardiness zone 3 and as far south as zone 8 all the way to Central American nations like Guatemala.
Growing Penstemon digitalis is also done commercially as a flowering ornamental plant, and many hybrids of the original species have been bred for hardiness and flower colors from violet to blue and magenta. Uses of Penstemon digitalis in display gardens are often tied to the fact that it is a tall plant and draws in a wide variety of pollinators, from bees to butterflies and hummingbirds. The plant generally requires little care and several strains will also grow well in conditions of limited fertility and moisture such as in rock gardens.
The main growing conditions that are recommended for Penstemon digitalis in general include that it be given relatively dry soil environments and exposure to full sunlight. Plants of the Penstemon genus are resistant to most pests and diseases. One of the problems that the perennial can have, however, is root rot, which will occur if the soil in which it is growing is continually water-logged and does not drain well.
Another key point to keep in mind with this variety is that hybrid species are not true perennials that can be grown year after year from seed. This is because a hybrid plant will revert to one of its parent plants with the next generation. True Penstemon varieties should therefore be grown if they are desired as a garden perennial, as many hybrids are plants with short life spans that tend to die off after their flowers drop. Over 275 species of the plant exist within the Penstemon genus as of 2011, so care should be taken in purchasing to determine if the plant is a digitalis and whether it is a hybrid.
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