Yellowspine thistle — May 2011

Yellowspine thistle

Yellowspine thistle plant

Yellowspine thistle flower

Yellowspine thistle seeds

Like a lavender starburst when viewed from above, the flower head of yellowspine thistle is somewhat reminiscent of a snowflake. The delicate appearance of these blooms provides quite a contrast to the rest of the plant, which is covered with stout yellow spines and therefore much less inviting. Also known as Santa Fe thistle, the scientific name of yellowspine thistle is Cirsium ochrocentrum. The genus Cirsium is the primary genus of North American thistles and the name comes from the traditional Greek name for a thistle plant, kirsion. From the Greek words ochos, meaning pale yellow and kentron meaning the center of a circle, the species epithet ochrocentrum refers to the conspicuous yellow spot in the center of the flower head before it opens. Yellowspine thistle is one of 13 native species of Cirsium in New Mexico and the only species I have found on the Preserve to date.

Yellowspine thistle prefers dry sandy to gravelly soil and commonly grows in prairies, pastures and disturbed areas like roadsides. It is a biennial (or a short-lived perennial) sometimes reaching four feet in height. In addition to a taproot, creeping lateral roots may develop, which are capable of producing new plants. One to twenty erect stems emerge from each root crown. Covered with dense woolly hairs, the stems are white in color. The leaves are relatively narrow and up to eight inches long with irregular lobes that look like triangular teeth. Each lobe ends in a sharp yellow spine. Hairs are also present on the leaf surfaces but are much more abundant on the lower surface. Therefore the undersides of leaves appear white whereas the upper surfaces are gray-green.

Solitary flower heads may be found at the ends of stems from May through August. A member of the aster family, Asteraceae, the blooms of yellowspine thistle consist of many small individual flowers tightly packed into a head. Cirsium ochrocentrum flowers have only disk flowers, each with pink, purple, or sometimes cream colored thin branching petals and smaller male and female parts. The flower head proper is typically wider than tall, but the base of the flower head (involucre) is urn-shaped. The numerous overlapping phyllaries on the outer surface of the involucre are quite distinctive, each with a white midrib and a substantial yellow spine.

Yellowspine thistle flowers attract a variety of insects to facilitate pollination. Once pollinated, each individual flower is capable of developing a seed covered by a smooth, brown dry fruit wall about 1⁄4” long that is topped with a conspicuous one inch white feathery plume that resembles a burst of fireworks.

With their abundant armor, thistle plants are quick to draw one’s attention. Native Americans were certainly well aware of yellowspine thistle and Zunis were known to use root infusions as a treatment for diabetes and as a type of contraception. In addition, infusions of the whole plant were used to treat syphilis. The Kiowa people used yellowspine thistle roots for food and used the flowers to cover fresh graves in an effort to keep wolves from digging up the corpses. They also prepared a decoction of blossoms that was applied to burns and sores. Many people today consider thistles in general to be undesirable weeds and indeed there are two non-native Cirsium species on the official New Mexico noxious weed list. Yet I believe our native species deserve some degree of appreciation if nothing else for their hardiness. In this year’s extreme drought conditions, yellowspine thistle is one of the few native plants that has consistently bloomed and added some much needed color to our landscape.

© 2011 Jerry Melaragno

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