Flora of North America species comparison

Species 106 (88 in the flora).

Seeds of Physaria contain hydroxy fatty acids, and some species, notably P. fendleri, are being intensively studied as a source of specialized, high-quality lubricants. The genus is notable for its relatively large number of local, often endangered, and edaphically-determined (usually calciphilic) endemics. Most of the genus Lesquerella (except for the auriculate-leaved species placed in Paysonia O’Kane & Al-Shehbaz) was recently united with Physaria, which is now much larger but monophyletic and morphologically coherent (I. A. Al-Shehbaz and S. L. O’Kane 2002). Where details of the trichomes are sparse, this is due to an absence of electron microscopy for these taxa (although the number of primary rays and some details are often visible at 10–30× with glancing light). The number of rays of the ubiquitous unicellular, stellate trichomes refers to the primary divisions immediately proximal to the center of the trichome. These primary rays are then typically furcate or bifurcate, often imperfectly so (2 + 1 branches, rather than 2 + 2). Trichome rays are usually appressed or parallel to surfaces on a short stalk; when the rays flare from surfaces, this is noted in the descriptions. Umbonate trichomes have a distinctive raised mound at the center; unless otherwise stated, trichomes are not umbonate. Tubercles are bumps or granules scattered along the rays and often over the center of the trichome. Flowering is likely to occur earlier than indicated in the descriptions, because specimens are typically (and optimally) collected when the fruits are nearly or fully mature, rather than when plants are only in flower. Raceme descriptions refer to mature infructescences unless otherwise noted. In Physaria, didymous is used as a term for fruit shape. A didymous fruit is inflated and appears as two balloons pressed together. The overall fruit shape is otherwise difficult to define and authors have traditionally referred to it this way. Replum shape and placement of the valve orifice are reported for only those taxa that were traditionally placed in Physaria, in the strict sense, where replum shape is sometimes helpful in separating species. The valves of didymous-fruited Physaria typically do not release their seeds; the valves and seeds disperse as a unit; species previously placed in Lesquerella freely release their seeds. The number of ovules reported, easily ascertained by counting funiculi, is most often greater than the number of seeds that occupy the fruit, either because of abortion or lack of fertilization. Species with mucilaginous seeds typically occupy steep and/or unstable habitats; when wetted, mucilaginous seeds can be “glued” onto optimal, local habitats.

(Discussion copyrighted by Flora of North America; reprinted with permission.)