Mentzelia decapetala, commonly known as tenpetal blazingstar, evening-star, or ten petaled western star is a biennial or short-lived perennial with large white flowers that bloom at night. It is native to dry areas of the western Great Plains in the United States and southern Canada. Its scientific name and many of its common names refer to the apparent ten petals of the flowers, the only species in the blazing star genus with such wide staminodes.
Description Tenpetal blazingstar is a bush-like perennial or biennial plant. Very rarely a plant may behave as an annual, blooming late in its first year and dying immediately afterwards, or spend a second year as an immature plant when weather or damage delays flowering. Its height is variable, but usually 15 to 91 centimeters (6 to 36 in) tall. It can sometimes be as tall as 100 cm (39 in). Plants may have a single stem or several and are upright or straight, however plants usually have just one stem. The stems are covered in a thin, white bark that peels off. They can branch only at the ends or along their entire length and are covered in hairs. It grows a deep taproot and is tolerant of drought conditions. The leaves of the tenpetal blazingstar range in length between 7.2 and 29.5 centimeters (2.8 and 11.6 in) with a width of 1.4 to 4.5 cm (0.6 to 1.8 in). The edges of leaves have coarse, irregular serrations and the surface of leaves feel like sandpaper. The rough texture of the leaves is produced by stiff, barbed hairs which will cause them to stick quite tenaciously to clothing or fur. The hairs are similar in shape to a Japanese pagoda when examined microscopically.
In its first year of growth tenpetal blazingstar has a basal rosette of leaves 10 to 20 centimeters (3.9 to 7.9 in) long and 1 to 3.5 cm (0.39 to 1.38 in) wide. They are oblong to oblanceolate, somewhat rectangular with rounded corners or having an outline like that of a reversed spear head with the point towards the stem and the broadest part past the midpoint. The edges are toothed, with the bottom of the indentations rounded and the lobes more pointed. The shape of leaves lower down on the stems is oblanceolate or elliptic, having two gentle elliptic curves and the widest part at about midway between the tip and base. Each of these lower leaves will have 16 to 26 teeth or lobes that are antrorse, curve upwards slightly. Leaves towards the ends of the stems are elliptic to lanceolate in shape, the latter like a spear head with the widest part below the midpoint. The bases of upper leaves might clasp the stem.
Flowering Single flowers are found at the end of the many branches. Each flower appears to have ten petals, but the inner five petals are in fact staminodia, a type of sterile stamen modified into a new structure. They are the largest of all the staminodia in the Mentzelia genus, averaging more than 2.5 mm in width. The showy flowers are white to palest-yellow in color. Each petal measures 4.7 to 7.5 cm in length by 1.3 to 2.27 cm broad with narrow points and are smooth and hairless on the outside. The center of the flower is filled with approximately 200 to 300 stamens, white to yellow in color and strongly clawed, curving inwards. The flowers open close to sunset, but they can be open early enough to be swarmed by foraging bees at the close of the day. The opening of the flower takes no more than one hour close to sunset, but will close up before the next day. Each flower lasts many evenings, opening each night and closing for the day, unless the morning is quite cloudy. The flowers release a noticeably pleasant scent. They may bloom early as June or as late as August, or on occasion even into October, in its native range. The fruit is an oblong cylindrical capsule 3–4.3 cm long and 1.2–1.7 cm wide with a tapering base, with the remnant of the dried style it has a resemblance to a stubby candle. When dry the capsule opens at the tip and shows there is only one chamber within the capsule containing a large number of seeds. The seeds are flattened lens shaped ovals 3–4 millimeters long. The edge has a papery wing 0.2–0.5 mm wide.
Taxonomy
Mentzelia decapetala was scientifically described by John Sims in 1812 with the name Bartonia decapetala. In 1892 it was moved to the genus Mentzelia by Ignatz Urban. It has no accepted subspecies or varieties. The species of Mentzelia are part of the family Loasaceae. Studies of the genetics of this and other species have shown that Bartonia is a monophyletic group and it is recognized as a section of Mentzelia. Within the section M. decapetala is most closely related to a 'subshrubby' group with species such as Mentzelia rhizomata, Mentzelia multicaulis, and Mentzelia pterosperma. It is also an outlier among the species that it is most closely related to in having highly modified wide staminodes, unlike its closest relatives. Where their range overlaps, M decapetala forms hybrids with Mentzelia laevicaulis. These hybrids have been found near Gardiner, Montana, but produce very little pollen and do not have viable seeds. Specimens of the species were collected during the Lewis and Clark Expedition in August 1804 near the Omaha village of Tonwontonga. This is now in Dakota County, Nebraska near the town of Homer. Alternatively, it may have been collected from an area of white chalk bluffs near the mouth of the James River. This specimen is likely taken to London by Frederick Traugott Pursh and lost. However, seeds and specimens were taken to London in 1812 by Thomas Nuttall. He had collected them along the Missouri River in 1811 and some of the seeds were planted at the garden of the Fraser Brothers at Sloane Square.
Synonyms Mentzelia decapetala has 7 synonyms.
… excerpt ends here. Continue reading the full article.
