Tansy Aster — September 2009

tansy aster plant

   Many roadsides and open areas of Deer Canyon Preserve are painted with mounds of purple this fall owing to a profusion of purple aster species. One prevalent such species is Machaeranthera tanacetifolia, the tansy aster. This genus name is derivedfrom the Greek word for sword, “machaira,” noting the tiny sword-shaped anthers (pollen sacs) in the flowers of members of this genus. The species epithet is based on a more easily observed characteristic of the plant, its leaves which are quite similar to those of the tansy plant (genus Tanacetum). Other common names for tansy aster are tansyleaf tansyaster, tansyleaf aster, prairie aster, and Tahoka daisy (seeds of this species are collected around Tahoka, Texas for commercial use).

   The tansy aster is an annual plant that typically grows in open, dry habitats and prefers sandy soil. Below ground it forms a taproot to acquire and store water and above ground the plant tends to branch extensively from its base. Consequently tansy aster plants are low-growing bushy plants, rarely exceeding 18 inches in height. Leaves are positioned in an alternate pattern along the stems and are highly dissected, giving the leaves a fern- like appearance. The leaves are a gray-green in color and form small spines at their tips.

tansy aster flower

   Flowers arise at the ends of stems and branches from June through October. As a member of the aster (or daisy, or sunflower) family, Asteraceae, each tansy aster flower is actually composed of dozens of individual flowers tightly compressed into a flattened head. Consequently, botanists have traditionally referred to this large group of plants as the “composites.” The outer ring of flowers (called ray flowers) each develops a long narrow petal or ray that is a pale purple to lavender color. The yellow central flowers are called disk flowers and each one has both male and female parts. After pollination, each female structure will develop a seed that will become surrounded with a dry protective fruit covering. Consequently after the other floral parts wither and fall away, the original flower head is left with a fuzzy round cluster of dry fruits, each containing a seed ready to be carried off by the wind (or some accommodating animal) as evident in the center of the photo below. This fruit structural arrangement and dispersal mechanism is reminiscent of the common dandelion, which is also a member of the aster family.

tansy aster seeds

   Because of its long flowering period, colorful flowers, and drought resistance, tansy aster is good choice for a native wildflower garden in Deer Canyon Preserve. It is available in local nurseries that feature native plants, but would have to be planted each spring since it is an annual (alternatively, one could rely on the tansy aster’s self-seeding abilities). It has been reported that tansy aster was used as a respiratory aid (dried root used as snuff to induce sneezing) by Navajo Indians and they used a decoction of the plant to treat stomachache. Hopi Indians also used a decoction of this plant as a general stimulant. Personally, I see no need to ingest this plant; its delightful and abundant flowers are perfectly sufficient to stimulate good cheer.

A Botanical View – The Asteraceae: An Evolutionary Success Story.

   How does one measure the evolutionary success of a particular group of organisms? There is no one single answer to this intriguing biological question, but one key factor must be diversity. And if number of different species is considered to be a meaningful measure of diversity then the Asteraceae (formerly Compositae) is the most evolutionarily successful of all plant families with 1535 genera and approximately 23,000 different species worldwide. It is clearly the most diverse plant family in New Mexico with 135 genera and 629 species. And of the 214 species of vascular plants on my far from complete Deer Canyon Preserve inventory, 53, roughly 25%, are members of the Asteraceae.

   As would be expected in a family with such diversity, there are relatively few general features that all species have in common. Members of the Asteraceae are mostly herbaceous plants, but several are shrubs and a few are trees. And they are found in a wide range of habitats, but are especially prevalent in temperate regions and open and/or dry habitats. The feature that all members of the family share is that their flowers are more or less densely aggregated into “heads” usually containing an indeterminate number of individual flowers. These heads often appear to be single flowers with a ring of “petals” (each such petal is actually an individual ray flower) that are subtended by one or more rows of “sepals” (each sepal is actually a bract, or modified leaf structure associated with a flower). The actual sepals associated with each individual flower in the head are highly modified usually into microscopic hair like structures forming what is called a pappus.

   Fortunately it is not necessary to be familiar with all the details and terminology associated with the floral structures to recognize most members of this family. The floral heads of familiar garden plants such as asters, zinnias, marigolds, chrysanthemums, dahlias, and sunflowers are all readily apparent as “composites.” For such a large family, it is surprising that relatively few species are of commercial importance other than as garden plants. The few food crops in the family include lettuce, endive, artichoke, and sunflower (seeds and oil). And among the Asteraceae there are only a few spice plants such as tarragon, chicory, and wormwood. Nevertheless members of this family contribute immensely to the diversity of plants in our natural landscape with their ubiquitous displays of evolutionary success.

© Jerry Melaragno 2009

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