Bulbs, Corms, Stolons, Tubers, Turions, and Bulblets
(Some of today’s images are from our earlier blogs in different contexts.)
Today’s topic is the suggestion of Pasco County Biologist Katie MacMillen. As John and I explore the hottest, driest, wettest, most disturbed, and most fire-prone habitats, we see a recurrent theme, as Katie noted: all manner of subterranean contrivances to allow plants to recover after trouble above…be it fire, sun, frost, flood, or fauna. We explored Halpatioke Park today for insects in a low area sometimes submerged sometimes dry. A perfect rhizome zone!
Patience please! A quick vocabulary lesson:
A rhizome is a horizontal stem usually beneath the ground level. Tasty example, ginger “root.”
A stolon is thin rhizome running across the ground surface. Familiar example, runners connecting grass clumps.
A tuber is a thick fleshy rhizome or an expanded rhizome tip. For instance, potato, or caladium “bulbs.”
A corm is a short thick vertical stem just below ground level. Garden example: Gladiolus “bulb.”
A bulb is a thin vertical stem surrounded by layers of thick fleshy leaf bases. Routine example: onions.
The common names for these structures are messed up and confusing.
In the local native flora we have it all:
The hunkiest local rhizomes might be those of Spadderdock, Nuphar, several inches in diameter and several feet long. In addition to surviving dry times, the big rhizome has an astounding second function. Spadderdock has pressurized airflow with some leaves taking in air and forcing it downward through the leaf stalk and then through the rhizome, eventually back out through other leaves.
Also well endowed rhizome-wise, Smilax may have more biomass below ground than above. It can pop up vigorously after a fire, often climbing the charred remains of its former competitors.
The aquatic emergent Sagittaria has textbook tubers, sometimes called “duck potatoes.” And they are tasty like a tater. So are the nuts (tubers) from the exotic weed, Yellow Nutgrass. Those who cook it call it Chufa.
Weeds are adapted to existential threats. Survival can be via tubers…ha ha you can’t yank, burn, or graze me…because I’ll rise from the ashes. The comely lumpy white tubers of Florida Betony (Stachys floridana) give the plant the name Rattlesnake Weed.
One of the worst weeds ever is Tuberous Sword Fern, combining the ferocious dispersal power of wind-blown spores with the immortality of tubers. Who said, “you can’t predict which introduced species might escape and become weeds”?
Some plants use tubers not just to persist, but also to spread, especially easy in aquatics such as the invasive pest Hydrilla, which in addition to float-away tubers has secondary smaller tuber-like units, called turions.
An odd tuber(ish) structure forms while a Live Oak is a mere baby, in its youth susceptible to ground-level hazards before achieving mighty oakdom.
Corms happen here too. For instance, Blazing Stars, Liatris species survive the trevails of exposed life via the dark underbelly of corms. If you buy garden Liatris you are most likely to buy corms marketed as “bulbs.” Likewise cormish is the Aroid Family, for example, Jack in the Pulpit and Arrow-Arum in Halpatioke Park today.
And then come bulbs, especially in the Lily Family and relatives: Catesby’s Lily and Spider-Lilies are all native local bulb makers. Our Halpatioke site today had bulb-bearing Crinum Lilies all abloom this morning mixed with rhizome-rich Cannas.
The introduced pink woodsorrel makes tiny bulb(let)s near the root-stem interface and elsewhere. The species makes no fertile seeds, the bulblets seem its sole means of reproduction and dispersal.
Why is all this underground business based on stems? Isn’t the dirt the domain of roots? Sort of. There are plants with creeping roots and thick storage roots, such as sweet potato, or its big-rooted native relative Largeroot Morning Glory. But stems have a more versatile, more diversified, more flexible structure than roots, so when evolution messes with a plant’s structure for a novel purpose, “stem” appears to be a better starting point than “root.”
Why do so many wetland species have so many rhizomes and tubers? Aren’t they safe in their nice moist marsh? For starters, where we encounter a species is not necessarily reflective of where it evolved. After all, most of Florida was under salty seas a few thousand years ago, so our marshy friends mostly evolved elsewhere before settling into Florida.
Secondly, a lot of shallow-water plants face intermittent drying. Pine flatwoods are full of summer ponds-winter meadows. Many evolved on shores or littoral shallows with fluctuating flooding, drying, and disturbance. Also, excessively deep water could be a foliage killer.
Yet another advantage of underground rhizomes for aquatics is a relentless war for space. When you look at an open shallow body of water there are immense single-species clonal clumps covering acres pushing and shoving with other massive clumps. Reminds me of 2017 politics, including the subterranean aspects. Victory requires spreading aggressively by rhizomatous growth, by rhizome fragmentation, and by territorial turions. Go forth and multiply. Seeds are good, but rhizomes are better at pushin’ and shovin’.