Evening Primrose is a biannual wildflower named for its habit of opening yellow blossoms at dusk. The four-petaled flowers are strongly scented with a sweet perfume that attracts pollinating moths. Evening Primrose is easily cultivated; it prefers acid, neutral, or alkaline, well — drained soils and requires full sun. It does best when not having to compete for soil or space.

Because the Evening Primrose is a biannual, the stem shoots up only in the second year of growth. In the first year, a taproot is put down. In the second year a sprout shoots up. Producing a biomass material only every other year is a definite drawback to its use as a biofuel; however, the density of its xylem material is significantly greater than that of the other candidate plants, actually giving the evening primrose a competitive output.

Evening primrose is grown commercially for its seed oil (treats asthma, arthritis, headaches). Consequently, there is a great bed of knowledge con­cerning its seed production, cultivation, and even some insights into strat­egies for making it provide an annual shoot.

Stem construction consists of a thin, barklike epidermis. The xylem cylinder has an XPR of 1.3 and a typical stalk diameter of 1.5 cm. Xylem material has a density of about 536 kg/m3, which makes it almost compa­rable to hardwood. The pith is a solid spongy inner core that rots after about 2 mo of drydown.

Evening primrose has a dense "stem," probably indicating a high per­centage of lignin, and a correspondingly higher heating value than the other SSPs. Being a biannual is a mixed bag. The harvest is less frequent, which is an advantage, but the population density of harvestable plants is only half of what an annual or perennial would be.