Crocanthemum nashii (Helianthemum nashii)
[Useful note: Helianthemum (Old World) and Crocanthemum (New World) are closely related, traditionally interpreted as a single genus. There are over 100 species.]
Today John (photomaster) and George (umbrella holder) continued a photographic project in Jonathan Dickinson State Park. John is developing panoramic images showing highlights of tour beautiful park. CLICK Zoom in, pan around.
On those fire-scorched sun-baked dunes grows a natural garden of wildflowers, most of them yellow. Delicate yet bright and vibrant today was Frostweed, Crocanthemum nashii, better known as Helianthemum nashii. The floral beauty of the “rock-roses, showy species of Helianthemum, have made them commercial horticultural delights. Most of the Helianthemums grow in hot, sunny, arid nutrient-poor habitats, making their curious subterranean relationships research-worthy. Some hook up, for instance, with desert-truffle fungi. Some share a fungal internet with oaks, which demonstrably benefit from the linkage.
That’s interesting, given that today’s pretty little flower grows on the world’s most sterile soil, often among oaks. Some species, perhaps all, Crocanthemum–Helianthemum species have a gelatinous covering on their seed coats. The gel houses fungi, which biologists in the 1950s and 60s interpreted as gifted to the seed from the mother plant to help nourish the youngster, especially with Vitamin B1, thiamin. Botanists in the 1970s brought that intergenerational fungus-among-us into doubt, although the tagalong fungi could perhaps establish relationships with the roots. Alternatively the fungi could merely be opportunists digesting the jello; then the main function of the goo could be in seed dispersal, or more likely to help with establishment in the arid habitats. Perhaps the best interpretation, not original with me, is the Mother Site Advantage, which is: the safest approach is to “stick around” Mom’s proven safety zone if suitable habitat elsewhere is spotty and widely separated.
Now move aboveground. First of all, the name Frostweed. Well, with their white hairs the plants look like a frosty mug. But don’t jump to conclusions! They also reputedly make “frost flowers,” i.e., pretty ribbons of ice at the stem base on freezing mornings. So you decide why to call them Frostweeds. Personally, I suspect the name originated with the hoary-looking foliage, and then the icy handle led writers into over-attributing our plants with frost-flower proclivities? Many plants do this, most notably, Verbesina virginica, sometimes dubbed Frostweed itself. That could engender confusion.
The hairs on the leaves and fruits presumably reflect that killer sand dune sun, although thwarting leaf eaters and maybe even catching/retaining water are possible as well. (The related and likewise locally native Crocanthemum corymbosum has the leaves notably darker green on top, and the fruit capsules is hairless.)
Crocanthemum nashii is almost restricted to Florida. Yet those who like to wonder,” how did that happen” might ponder a small geographically isolated population yonder in southern coastal North Carolina, separated from the general population by Georgia and South Carolina.
One final oddity. The showy yellow flowers attract diverse pollinators, but that’s not enough. The plants have a second way to make seeds. Later in the season (C. nashii) or at the same time (C. corymbosa), in addition to those regular open flowers, come small, closed non-showy (cleistogamous) blossoms that quietly self-pollinate out of sight and out of mind. Differences, if any, in the gel-covers and germination characteristics of seeds derived from the two flower types might make an interesting study.
Note: To dig in on the oak relationship, start here