Frostweeds  & the Mother Site Advantage

15 Apr

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.

helianthemum nashii far

Frosty on the burnin’ sands, as they looked today.  (All photos this week by John Bradford)

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,  CrocanthemumHelianthemum 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.

Helianthemum nashii close

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.

Helianthemum nashii close 2

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



Posted by on April 15, 2016 in Uncategorized


6 responses to “Frostweeds  & the Mother Site Advantage

  1. theshrubqueen

    April 16, 2016 at 8:42 am

    Any theories on why the flowers tend towards yellow?

  2. George Rogers

    April 16, 2016 at 9:32 am

    Yes….in a big general way…bees like yellow, presumably originating in the color of pollen. Flowers use a lot of yellow advertising for bees. Why there is such a concentration of yellow flowers on the JD Park scrub and in other scrubs…sometimes…must have to do with pollinator availability relative to place and time.

  3. theshrubqueen

    April 16, 2016 at 1:12 pm

    Hmm, maybe an ancient mechanism?

  4. George Rogers

    April 16, 2016 at 4:39 pm

    Yes absolutely

  5. xXtheoneandonlyshrubkingxX

    April 19, 2016 at 7:58 am

    do you think colorization has to do with pollinator choice?

    • George Rogers

      April 19, 2016 at 8:28 am

      Yes. Here is my take, not altogether original, and flavored with biased interpretation. On a white sand scrub I’d tend to think pollinators are a limited commodity. Bees would probably be the main ones. Bees seem to have a thing for yellow. That might tend to put a premium on yellow flowers (frostweeds, various legumes, prickly pear, Hypericum reductum, various Asteraceae), although of course there are others. So, merely getting bees to begin with might be a large factor in the equation. Want bees?—Show yellow! (And some butterflies join the party.) The remarkable resemblance in flowers open in some times and places could merely be convergence around the question of, “what sort of flower works best here and now,” or maybe sometimes, speculatively, sort of a “Mullerian Mimicry” along the lines of mimicking the other species or species cluster already drawing pollinators. Once the pollinators arrive, I guess then competition begins. Maybe a little like shoestores in the mall…first let’s get shoe shoppers to the mall (lots of shoes, great food court), then once they arrive, specialize a little to hold down competition—ladies shoes, athletic shoes, bigger flowers, smaller ones, different fragrances, brighter yellows, different times of season or times of day. Not stating fact! Just having fun.


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