Two subpecies of Heterotheca sessiliflora in Marin?

Another look at Marin plants know as Heterotheca sessiliflora ssp. bolanderi or are they ssp. bolanderioides

by Doreen Smith

Last year Heterotheca sessiliflora ssp. bolanderi was featured on the Marin Chapter CNPS website as plant of the month. Several of us had observed two large patches (clones?) of this plant on Pt. Reyes that looked different from any we’d seen before on mainland Marin.  We were curious to learn why. Photographs were sent by Amelia Ryan, NPS, to Emeritus Professor John C. Semple, a veteran expert in the study of the genus Heterotheca.   His comments were helpful in elucidating our understanding of what is typical Heterotheca sessiliflora ssp. bolanderi which it seems the PORE plants fit. The inland ones may be better understood as ssp. bolanderioides or even ssp. echioides, sensu the Jepson Manual #1 and also in #2.
 
The supposed by us “ssp. bolanderioides“ grows in dense clumps in grassland such as on Big Rock Ridge, Nicasio Ridge and the N. slopes of Mt. Tamalpais. The plants are found in areas adjacent to serpentinite ridges but not as part of the usual strictly-serpentinite flora of this area. The clustered mass of vertical stems are each terminated by several flower heads.
 
In contrast is the widely-spreading, prostrate habit of ssp. bolanderi on the sandy flats at Pt. Reyes. Each flower head is solitary and terminal on an erect peduncle.

Photos by Vernon Smith

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