Frostweeds (Helianthemum species)
Pinweeds (Lechea species)
Scrub is arguably (but let’s be agreeable) the most botanico-rific Florida habitat. Here is the oddest, oldest, and most diverse ecosystem in town. No space here to wax lengthy on scrub, so let’s knuckle down and concentrate on four interrelated mysteries of the sugary sands:
1. How can clumps of Frostweeds (Helianthemum species) abide in in the middle of parched, sun-baked, nutrient-poor, almost-lifeless white sand patches?
2. How can Pinweeds (Lechea species) do the same thing?
3. Why do the two do it together?
4. Why is there always broken glass in those habitats?
All scrub plants tolerate an extreme habitat, but helianthemums and lecheas occupy the extreme of the extreme where cacti might seem comfortable and to some extent are, yet these brave little plants don’t look like tough cacti at all. Lechea is extreme-looking in a different way, but helianthemums look like pretty garden flowers with yellow blossoms above silvery-tinted foliage. Some Helianthemum species are commercial garden flowers.
I can’t speak about broader geography, but in my favorite scrub sites, Helianthemum and Lechea hang out together like Fred and Barney. Remember that—it’s important.
The togetherness becoems more interesting with the knowledge that the two are related, both belonging to the Rockrose Family. : The kinship helps explain their mutual affinity for Sahara conditions. It’s a family trait. In fact, species of Helianthemum are native to the Sahara itself.
Sometimes, as I hammer to students, when a single species puzzles you, look to its relatives for insights. You can’t generalize 100%, but you can make great educated guesses. If I know a child is a Rockefellar, there’s probably a trust fund. If a critter belongs to the Canine Family it is not likely vegan. If a plant belongs to the Cistaceae, seek it on sunny sand and stones. A center of diversity for Cistaceae is the dryish, sandish, rockish, sunnyish Mediterranean Region, and wherever else you find them from the Yukon to Chile, they are probably in the local “desert.” Even in the garden world, Cistaceae are known as rock garden dwellers. This is the Rockrose Family after al. Want to learn a new vocabulary word? Chamaephytes (KAM-eh-fights) are plants that hide buds safely underground, and many Cistaceae are chamaephytic. Many grow in clumps that catch debris in the wind to become self-mulching, as in the photo below.
A particularly noteworthy adaptation to harsh living prominent among Cistaceae are mycorrhizal fungal helpers. Mycorrhizae (my-coe-RIZE-ee) are fungi sharing symbiotic relationships with plant roots, helping the roots snag nutrients and even water. Ever wonder why so few scrub plants succeed in gardens? I don’t really know but suspect most require a soil-mycorrhizae context difficult to simulate in the back yard. In Cistaceae some of the mycorrhizal fungi are truffles. Not the chocolate candies, but the fungal tubers so beloved by hogs and gourmets. Now truffles are costly, so there’s always been interest in truffle farms. Cistaceae, including Helianthemum, have received serious research as possible host plants for the tasty tubers. Hey there’s an idea, Florida is open for business! Boot out the scrub jay deadbeats and convert all that useless scrub to tax-paying truffle farms.
No e-mails please (pro or con)—-Just kidding you know.
All this said, a question emerges. If Cistaceae depend on mycorrhizae to live where nobody else will, and if two of our most extreme open-sand scrub dwellers both belong to Cistaceae, is their togetherness rooted in mutual mycorrhizae? Does Helianthemum arrive with mycorrhizae in its seeds (yes—stay tuned), and thus set the stage for its cousin Lechea to tag along? Do the two share a single mycorrhizal network?
In species of Helianthemum the seed coat has a gummy outer layer inhabited by the friendly fungus which rides along with the seed. The relationship is so intimate and necessary that seedlings of Helianthemum do not even form root hairs, as the fungus apparently assumes their function.
By the way, Helianthemum is othewise adapted to extremes; it has silvery reflective foliage bearing star-shaped hairs, thus the “frost” in the name. It looks a little hoary. Some self-propagate from subterranean rhizome fragments. Species of Helianthemum make “cleistogamous” (kleist-OG-ah-mus) flowers in addition to their conventional yellow blossoms. Cleistogamous flowers are tiny and non-showy, and self-pollinate without opening.
Lechea is just odd. The small variably fuzzy leaves appear fairly drought-proof. The flowers are tiny pinheads. I never see them open. Maybe they do not have to open much, as Lechea has a reputation for self-pollination. My personal point of origin, the University of Michigan Herbarium, has an interesting Lechea comment on their web site: “The flowers rarely open, but are reported to do so in early morning on bright days.” I just don’t get up early enough.