Beach sun cup
Camissonia cheiranthifolia is one of the few plants that bloom year around along our coast. It is found most commonly on the unstable, sandy hillocks immediately in-shore from the beach. It can also occasionally found on disturbed sandy soils away from the immediate coast, but this is very rare. Its range is from southern Oregon to just into Baja. In the northern part of it range it is basically a perennial herb. It becomes somewhat woody in the southern portion of its range. Being somewhat in the middle, it can be either in our chapter area (San Luis Obispo county). It is quite variable here. Behind the windy beaches it’s a flat ground cover, while in sheltered areas it is taller and less spreading.
I’ve seen a few green plants with no surface hairs, but most of our plants are more or less hairy. Some petals have red spots at their base while others lack these spots. What looks like a very large bud arising from the angle between the leaf below the flower and the stem in Bonnie’s drawing is actually the elongate fruit, which becomes twisted as it matures. Flower size is also quite variable.
Before 1969 beach sun cups were in the genus Oenothera. At that time the common name applied to this entire genus was “evening primrose.” So, Camissonia cheiranthifolia would have been called “beach evening primrose” or simply and misleadingly, beach primrose. However that common name is quite misleading; primrose is a name better applied to a totally different and unrelated group of plants in the true primrose family (Primulaceae) which include the shooting star and the pimpernel.
The only trait that sun cups and true primroses share is their general tubular shaped flowers. Sun cups (with other members of its family, Onagraceae) have four separate petals instead of the five fused petals found in the primroses. In fact, the flowers of Onagraceae, including the sun cups, have a distinctive set of characteristics. They produce flowers that possess four sepals, four petals, eight stamens, attached to the top of a generally thin, elongated ovary which displays a four-parted structure.
The distinctive characteristics of the Onagraceae family can be summarized as CA4 CO4 A8/G 4 . CA is short for calyx which is the collective term for the sepals. CO stands for the corolla, the collective term for the petals. A is the abbreviation for andrecium, which translates as all the “male things,” the stamens. G stands for gynoecium (female thing), which represents the four-parted ovary, style, and stigma. The circled 4 indicates that the four subunits (carpels) that make up the gynoecium are fused into a single pistil.
Why did Dr. Peter Raven separate the sun cups from the evening primroses when they share so many family characters? First and most easily observed is the stigma. A look at Bonnie’s drawing will show it to resemble a single, wide, hemispherical cap as opposed to the four hair-like stigma branches found in the true evening primroses. A second trait is harder to determine. True evening primroses produce their flowers at dusk and bloom through the night and fade in the morning. Sun cup flowers open at dawn and bloom during the day. This means the two genera have different pollinators since their flowers are open at different times of the day.
Evening primroses would be expected to be visited by night-flying animals such as moths whereas sun cups would be visited by day-flying ones. While researching tidbits to include about beach sun cups, I came across the discussion of the species in the book by Mary Coffeen titled Central Coast Wild Flowers. In it she reprints part of an article about the Morro Bay Sand Spit by my friend and former Cal Poly professor, Wayne Williams. In it he describes the pollination of beach sun cup and as follows:
“The plant’s bright yellow flowers cover new sand deposits everywhere along the sand spit, enhancing dune stability. Its blossoms face down wind. The pollinator is an exceptionally large bumblebee (Bombus sp.). We have all heard how bumblebees manage to fly despite the aerodynamic engineering theory that would render them landbound because of their weight and size. These bees deftly approach the beach primrose flowers by flying upwind for greatest flight stability. Their powerful thorax muscles and large size allow them to survive within this niche, gathering food and pollinating, because of the downwind direction of the primrose corollas. Since the primrose is decumbent where wind speed is slowest, the bees can also work over large territories. I have watched these bees and have never seen any other species pollinating beach primroses at the sand dunes. This symbiosis between plant and insect allows both the plant and the bumblebee to thrive and reproduce.”
Just imagine how much observation time required to allow one to come up with this kind of natural history fact. There are lots more yet to be discovered. That’s why natural areas like the Elfin Forest are so important.