notes A partially dissected flower of Streptanthus cordatus var. piutensis...the petals and abaxial sepals have been removed, showing the three unequal-length stamen pairs (blue arrows = short lower/abaxial stamen pair; green arrows = middle stamen pair; pink arrows = long upper/adaxial stamen pair). This characteristic of having three unequal stamen pairs does not occur throughout the genus, and is among the diagnostic characters for S. cordatus. Interesting that for all three stamen pairs: the shorter the stamen (and filament); the longer the anther! Also, at the time of this photo, the longest stamen had its (shortest) anther almost fully dehisced; while the shortest stamen had its (longest) anther still unopened...with the middle pair at mid-dehiscence. Meanwhile the stigma appears to have freshly begun its receptive stage...while the style has not yet begun to elongate. The geometry and temporal sequence of events within these individual flowers (and the bottom-to-top sequence of flowering along the raceme) is fascinating...as are their roles in the larger context of pollination, and the rich relationship to the correlated morphology and behavior of their pollinating insect-visitors.
---------------------------------------
This flower came from a plant in the area of the type locality for S. cordatus var. piutensis...see this BHL link for the original description by John Thomas Howell, published in 1963. As Howell points out, var. piutensis differs from the nominal variety in its taller stems, more woody caudex, narrower cauline leaves, and typically smaller flowers.
The plants in this population keyed unambiguously to S. cordatus var. piutensis in the Jepson eFlora Key to Streptanthus, the FNA key, and Reed Rollin's 1993 'Cruciferae of Continental North America'. The diagnostic characters are: cauline leaves sessile, clasping-auriculate; racemes ebracteate and lacking a terminal 'flag' of sterile flowers; fruit glabrous; perennial; all stamens fertile; cauline leaves reduced distally; fruit spreading to ascending; stamens in 3 unequal-length pairs (not tetradynamous); basal leaves dentate; mid-cauline leaves lanceolate and acute.
Another informative reference for this taxon is Greene & Sanders(2006).
The plants in this population were growing on a reddish substrate of scree, talus, and clay derived from a geographically localized Mesozoic-age roof pendant of gabbro...see the interactive CA geologic map at this link (and enter lat/log coords 35.564 -118.492 in the 'Esri World Geocoder' field). See also the 2015 paper 'Gabbro Soil-Plant Relations in the California Floristic Province' for an informative discussion of gabbro soils and plant endemism (the Piute Mountain gabbro and S. cordatus var. piutensis are briefly discussed on page 80). Much detail on the geology on the olivine gabbro body south of Bodfish can be found in this 1987 USGS report (see pg. 7, maps on pp. 38 & 39).
