Plants of the month include Calystegia purpurata and Calystegia occidentalis, two western morning-glory species. Already I have seen Calystegia purpurata flowering on a chain-link fence by the northbound San Rafael Highway 101 exit. Mostly the flowers of this species are white with purple lines, fading to pink, but some plants have pink flowers from the begining and fade almost red-purple. This gives the reason for the Latin specific epithet.
Marin has two subspecies of Calystegia purpurata. The most common is ssp. purpurata, a vine seen trailing over other vegetation. The other subspecies is the rarer fleshy, more-compact coastal-bluff plant, ssp. saxicola, for which Marin appears to be the southern limit of distribution. It grows in the coastal prairie at Point Reyes. The best examples we have can be seen on the banks of the trail down to McClures Beach and on Tomales Point, where they flower in early summer.
As the flowers of all our local morning-glories are very similar in shape and color, the key features used to identify the species are vegetative. You need to check the hairs present (or not) on the leaves, the leaf-shape, and the position and shape of the sub-floral bracts. At one time C. purpurata and C. occidentalis were thought to be the same species. Amongst the now-apparent differences is that C. occidentalis is hairy, has short trailing stems, and bracts positioned very close to the calyx. It only flowers for a short period of the year. In C. purpurata the bracts are well below the calyx and it flowers for as long as moisture is available, which on the coast can be most of the year.
The hills above Old St Hilary’s in Tiburon have C. purpurata ssp. purpurata growing on the lower slopes and C. occidentalis on the uplands. Marin has three other species of California native Calystegia: C. collina, C. subacaulis, and C. soldanella. The large-flowered, white morning-glory from Stinson Beach once thought to be native C. sepium ssp. limnophila is now known to be the European introduction Calystegia silvatica ssp. disjuncta.
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| Calystegia purpurata ssp. purpurata by Palomarin Trail, Point Reyes (Photo by Doreen Smith) |
Calystegia purpurata ssp. saxicola (Photo by Doreen Smith) |
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| Calystegia purpurata ssp. saxicola? at Chimney Rock (Photo by Doreen Smith) |
Calystegia occidentalis ssp. occidentalis (Photo by Doreen Smith) |