aster family

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Meet Liatris microcephala

The aster family has a lot to offer. It’s really no surprise considering that Asteraceae is the largest family of flowering plants in the world with as many as 33,000 species. Certainly its ecological importance is substantial. It also contains, arguably, some of the most beautiful and attractive plant species, as well as a significant selection of useful plants from a human perspective. When a plant family is this big, it is essential to subdivide it into smaller groups in order to better understand it. The subject of this post finds itself in a tribe within the aster family called the thoroughwort tribe or Eupatorieae – home to other familiar genera like Ageratina, Ageratum, Eupatorium, Eutrochium, Conoclinum, and Stevia.

Liatris is a North American genus that includes around 37 species and at least 12 naturally occurring hybrids. All of these species are found east of the Rocky Mountains – scattered across the Midwest, in the northeastern and southeastern regions of the United States, as well as north into Canada and south into Mexico. While there are a couple of species found within the Rocky Mountain region, there are no species of Liatris found west of the Rockies. One species is found in the Bahamas.

Commonly known as gayfeathers or blazing stars (not to be confused with the blazing stars of the Mentzelia genus in the family Loasaceae), Liatris is a group of perennial plants with upright, mainly unbranched stems that flower from the summer into the fall. After dying back to the ground in the winter, they emerge in the spring from elongated or globular corms, their narrow leaves giving the appearance of a tuft of grass. Flowers occur in the upper portions of upright stems and are held in bell-shaped or cylindrical involucres. They lack ray florets like those of a typical aster flower. Instead, each flower is composed only of a series of small disc florets which can give them a button-like appearance. Flowers come in shades of lavender, magenta, pink-purple, and rose-purple (sometimes white).

grass-like foliage of Liatris microcephala

Plants in this genus vary in height, with the tallest reaching over 5 feet. My affinity for diminutive plants draws me to some of the shorter plants in this group, particularly Liatris microcephala or smallhead blazing star. Other common names for this plant include dwarf blazing star and Appalachian blazing star. This species has very slender, linear leaves and looks a lot like a little bunchgrass for much of the growing season until its flower stalks start to emerge in midsummer. These stems can rise to 2 feet tall or more, but are often much shorter, especially in the lean soils that I grow them in here in Idaho. Linear leaves lacking petioles are alternately arranged along the length of the flowering stems. Flowers are rose-purple or lavender and composed of only 4 to 6 disc florets. They flank the upper portion of the upright stems, and gradually open from the top down from mid to late summer into the fall.

The fruits of Liatris are slender, ribbed achenes with a short, bristly pappus attached that is either feathery or barbed. The pappus of L. microcephala is minute and bristly. Once mature, the fruits detach from the plant and are blown around by the wind, sometimes grabbing on to the fur of passing animals.

smallhead blazing star (Liatris microcephala)

L. microcephala has a relatively limited natural distribution, occuring mainly in the southern Appalachian Mountains from western North Carolina and Kentucky, south to western South Carolina, north and central Georgia, and into northern Alabama. It prefers dry, rocky, slightly acidic soils, but can tolerate other soil types as long as they are well-drained. It prefers full sun and tolerates high heat and humidity. Its tendency to grow in rocky outcrops makes it a good rock garden plant. It is also used on green roofs. Like most other plants in this genus, L. microcephala needs well-draining soils particularly during the winter, as corms can rot out when they stay wet over prolonged periods.

A Chicago Botanic Garden plant evaluation report includes Liatris in a list of perennials that first gained popularity in European gardens before finding favor in the North American horticulture industry. In spite of being native to North America, gardeners on this continent looked to plants from other parts of the world to fill their gardens. Now, as trends shift towards native plants and habitat gardens, plants like native blazing stars which are visited by a variety of insect species and whose seeds are consumed by birds, are an obvious choice. They are relatively easy to grow and care for, and there is a wide selection to choose from, including cultivars. Though not native to the west, blazing stars are great plants for gardens in our region due to the drought-tolerance that is common in this group. Water conservation is of particular importance in the semi-arid west, and L. microcephala, with its penchant for growing on rocky outcrops is particularly drought tolerant. Apart from that, it’s just a beautiful, little plant and one that I will continue to grow, with the dream of someday seeing it in its natural setting.

smallhead blazing star (Liatris microcephala)

See Also: Meet Erigeron linearis

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Flowers Growing Out of Flowers (Things Are Getting Weird Out There)

I’m sure that anyone living through the events of 2020 would agree, these are truly wild times. So, when I stumbled across some purple coneflowers that appeared to be growing flowers out of flowers, I thought to myself, “Of course! Why not!?!” The world is upside down. Anything is possible.

As it turns out, however, this phenomenon occurs more frequently than I was aware. But it’s not necessarily a good thing, particularly if you’re concerned about plant health. We’ll get to that in a minute. First, what’s going on with these flowers?

Flowers in the aster family are unique. They have the appearance of being a single flower but are actually a cluster of two types of much smaller flowers all packed in together. Purple coneflower (Echinacea purpurea) is a great example of this. Its flower heads are composed of dozens of disc flowers surrounded by a series of ray flowers. The minuscule disc flowers form the cone-like center of the inflorescence. The petals that surround the cone are individual ray flowers. This tight cluster of many small flowers (or florets) is known as a composite. Sunflowers are another example of this type of inflorescence.

Flowers are distinct organs. Not only are they the reproductive structures of flowering plants, but unlike the rest of the plant, they exhibit determinate growth. Flowers are, after all, plant shoots that have been “told” to stop growing like other shoots and instead modify themselves into reproductive organs and other associated structures. Unlike other shoots, which continue to grow (or at least have the potential to), a flower (and the fruit it produces) is the end result for this reproductive shoot. This is what is meant by determinate growth. However, sometimes things go awry, and the modified shoots and leaves that make up a flower don’t develop as expected, producing some bizarre looking structures as a result.

An example of this is a double flower. Plants with double flowers have mutations in their genes that cause disruptions during floral development. This means that their stamens and carpels (the reproductive organs of the flowers) don’t develop properly. Instead, they become additional petals or flowers, resulting in a flower composed of petals upon petals upon petals – a look that some people like, but that have virtually nothing to offer the pollinators that typically visit them. Because of their ornamental value, double-flowered varieties of numerous species – including purple coneflower – can be found in the horticultural trade.

double-flowered purple coneflower

Genetic mutations are one way that odd looking flowers come about. It is not the cause, however, of the freak flowers that I recently came across. What I witnessed was something called phyllody and was the result of an infection most likely introduced to the plant by a leafhopper or some other sap-sucking insect. Phyllody, which has a variety of causes, is a disruption in plant hormones that leads to leaves growing in place of flower parts. As a result, the flowers become sterile and green in color. In the case of purple coneflower, leafy structures are produced atop shoots arising from the middle of ray and/or disc florets. In other species, shoots aren’t visible and instead the inflorescence is just a cluster of leaves. In a sense, the reproductive shoot has returned to indeterminate growth, having switched back to shoot and leaf production.

Phyllody can have either biotic or abiotic causes. Biotic meaning infection by plant pathogens – including certain viruses, bacteria, and fungi – or damage by insects. Abiotic factors like hot weather and lack of water can result in a temporary case of phyllody in some plants. Phyllody plus a number of other symptoms made it clear that the purple coneflower I encountered had a fairly common disease known as aster yellows. This condition is caused by a bacterial parasite called a phytoplasma, and is introduced to the plant via a sap-sucking insect. It then spreads throughout the plant, infecting all parts. The phyllody was a dead give away, but even the flowers that weren’t alien-looking were discolored. The typical vibrant purple of the ray flowers was instead a faded pink color. The flowers that had advanced phyllody – along with the rest of the plant – were turning yellow-green.

This inflorescence isn’t exhibiting phyllody yet, but the purple color in the ray flowers is quickly fading.

Hundreds of plant species are susceptible to aster yellows, and not just those in the aster family. Once a plant is infected with aster yellows, it has it for good and will never grow or reproduce properly. For this reason, it is best to remove infected plants from the garden to avoid spreading the infection to other plants. As cool as the flowers may look, infected plants just aren’t worth saving.

Further Reading: