Pityopsis graminifolia, or narrowleaf silkgrass, is a fibrous-rooted flowering perennial named for the silvery hairs that cover its stems and give a silky appearance. Pityopsis graminifolia flower heads have characteristic ray and disk florets, and the linear-lance-shaped leaves of the plant often appear grasslike. This plant is a part of the Asteraceae family, also known as the daisy or sunflower family. Although Pityopsis graminifolia is commonly found in the southeastern United States, its distribution also includes some parts of Central America. Because Pityopsis graminifolia is drought resilient and can grow in nutrient-deficient soil, it flourishes in many different environments, including coastal sandhills, forests, longleaf pine ecosystems, and roadsides.
Description
Pityopsis graminifolia is also known as narrowleaf silkgrass, Silver-leaved aster, Grass-leaved goldenaster and Silky golden-aster. Many of its common names reference grass because the plant can be mistaken for grass. Its leaves are often basal and range in length from 10 to 35 cm (3.9 to 13.8 in) and reach between 3 and 10 millimeters wide. Each plant has 1-5 stems that reach around 20–80 cm in length, covered in short, alternating stem leaves. The characteristic trait of narrowleaf silkgrass, and the reason for the term ‘silky’ in its common names is the silvery hairs that cover the plant stems. Pityopsis graminifolia has yellow composite flower heads, which are about 2.5 cm wide, with both ray and disk florets. These flowers turn into pappi—another common feature of the Asteraceae family— which are small dry fruits that contain the matured ovary in the form of a seed, with hair-like structures on the top that act as a parachute to disperse the seed with the wind. These pappus have two series. The inner series has barbed bristles ranging from 5-9mm and the outer series has shorter 0.4-0.9mm bristles.
Reproduction
Sexual reproduction
Pityopsis graminifolia, a part of the Asteracea family which includes sunflowers, asters, daisies, and marigolds, has ray and disk florets in each flower head. The disk florets are perfect and the ray florets are pistillate. The disk flowers are protandrous, meaning that the florets release pollen before the female reproductive parts become receptive. This dichogamy, in addition to self-incompatibility strategies, make it difficult for Pityopsis graminifolia to self-pollinate, except through geitonogamy. On each capitulate flower there are on average 20-70 florets, with 10-16 ray florets and 30-40 disk florets. Flowering times vary greatly based on subspecies and location, but the plant often flowers between late summer to early winter. Pityopsis graminifolia is pollinated by bumblebees and lepidopterans. Pityopsis graminifolia produces wind-dispersed achenes fruit that are fusiform with translucent, thin ridges running along the sides of the fruit.
Cloning Although Pityopsis graminifolia is capable of sexual reproduction through outcrossing, much of its population upkeep comes through cloning through rhizomes to create individual ramet plants. The rhizomes run underneath the soil, with new plants branching off at axillary buds to grow above the surface to form new plants. In fact, Hartnett (1987) documented that an experimental study site population was entirely maintained through cloning over a two year period. During that time, no seedlings were successfully established.
Fire-enhanced flowering Pityopsis graminifolia’s reproduction is oftentimes closely linked to growing-season fires, especially in longleaf pine forests. These fires are often the result of lightning strikes. Pityopsis graminifolia has the ability to survive forest fires because their apical shoots lie 2–3 cm below the soil, which provides a protective layer against the fire’s heat. In addition to a protective soil layer, Diaz-Toribio (2021) discusses how nonstructural carbohydrate stores in plants, which Pityopsis graminifolia has a large concentration of in comparison to other species in longleaf pine forests, promote resprouting after a fire. Because this plant can survive fires, its fire-enhanced floral induction is an adaptive trait to help it better compete against other species. Normal seedlings do not compete well against adult plants and have a successful establishment rate of 1-3%. By waiting until immediately following a fire, Pityopsis graminifolia can capitalize on the lack of underbrush and the increase in sunlight from canopy removal to release seeds that have a higher chance of survival. This decreases the energy cost of reproduction when seedling mortality would be high.
Habitat Pityopsis graminifolia grows best in sandy ecosystems with full sunlight and limited canopy competition. It often chases full sun by growing in sandhill communities, roadsides, or the edges of woods, areas that might not be ideal for other plants because of nutrient poor soil but that Pityopsis graminifolia can grow well in. Pityopsis graminifolia is also drought tolerant. Pityopsis graminifolia is commonly a dominant species in longleaf pine communities because the frequent fires limit the growth of woody plants, which would normally block most of the sunlight by creating dense canopies. It can grow in the piedmont and mountains, but these habitats are not ideal because it grows best in soil with little to no humus. This species occasionally is used for ornamental landscaping.
Distribution Pityopsis graminifolia is most commonly found in the southeastern United States, especially Florida. However, this plant is not limited to the southeastern United States. It reaches as far north as Ohio and as far west as Texas. Although less common, detached populations can also be found in Central America, the Bahamas, and the Caribbean, even as far as northern Honduras.
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