Friday, March 31, 2006

one-sided bluegrass, Poa secunda ssp. secunda, Feb–May, Native

Poa is the largest genus (ca. 500 species) of the grass family Poaceae (ca. 10,000 species worldwide), the fourth largest flowering plant family after Orchids, Asters, and Legumes. Represented by 91 taxa (species, subspecies, and varieties) at Jasper Ridge, Poaceae is the second largest family on the Preserve; Asteraceae is the largest.

Poa secunda is highly variable and grows in many vegetation types from sea level to 12,500 feet, near the top of Sierra Nevada peaks. Our form was formerly called Poa scrabella. In a cool, wet spring such as 2005 (March to early April), it can be abundant on serpentine, where it is particularly beautiful, leaves and stems having a blueish cast. Lemma tips are typically purplish. When flowering, called anthesis, stamens become exserted, dangling from their florets in the breeze, imparting an open hoary appearance to the plants. Leaves are not abundant and die back soon after flowering, at least in lowland grasslands. Exsertion of staminate and pistillate parts on the path to disarticulation and seed dispersal occurs in many but not all grasses, and contribute to the changing appearance of grasses through their developmental cycle. These transformations can confuse the observer. Poa secunda has an early, tightly-appressed, upright inflorescence whose branches may relax, often becoming open and airy, during full bloom in March. Plants typically metamorphose as the stamens wither, turning brownish-tan causing the inflorescence to appear shaggy. The stamens soon fall off. Some inflorescences persist as a tight flowering head of glumes and a few florets (as shown in the illustration).

The ubiquitous Poa annua is also present on the Preserve in roads, including those through serpentine, and other disturbed areas.

Name: ancient Gk name | turned to one side (which is not obvious).

Illustration from Intermountain Flora