Polygonella

Wireweeds, Jointweeds,  Octoberflowers

Polygonella species

Polygonaceae

Two weeks ago John and George botanized a morning away in Jonathan Dickinson State Park near Hobe Sound.  The open sand areas looked like foam on the sea thanks to Octoberflower (Polygonella polygama).  This week we had chores in and near  Savannas Preserve State Park at Jensen, where another Polygonella,  Stout Jointweed (P. robusta) made the sugar sand whiter.  It is a Florida endemic or nearly so.  These and additional Polygonellas help keep Florida beautiful with their delicate mostly-white bountiful blossoms, which are on separate male and female plants in Octoberflower, but either bisexual or mixed male and female on single plants in Stout Jointweed.  The flowers of both start out white and turn to pink or rose or deeper shades, creating  impressionistic  color drifts in dense Polygonella meadows.

Octoberflower in September (by JB)

Altogether there are 11 species of Polygonella, all of them in the eastern and southern United States, most represented in Florida.  As a group, they tend to like dry sunny sandy places,  such as open areas in scrub, sometimes sandhills, or disturbed places.

Outside of our usual haunts, Polygonella basiramea and P. myriophylla are federal listed endangered Central Florida scrub endemics.  Polygonella myriophylla maintains a clear zone around itself by emitting natural herbicide(s).  This “allelopathic” ability probably occurs in other species as well, but rare and endangered species attract research.  Our Treasure Coast-ish species have bare zones around them too. Do they poison the competition?  Or do they merely grow the hot bare sand  where others fear to tread?  Or do they take advantage of the allelopathic “moats” of naturally herbicidal third parties, such as Florida-Rosemary?  All that would be fun to study.

Take a close look at a Polygonella…hey, there’s something “wrong” with that plant.  Oh, I know, the branch points are between leaves rather than immediately above the leaf-stem junction as in the rest of the plant world  (The branches originate normally but remain fused in part to the stem giving the illusion of arising midway between leaves.)  Knowing this, now you will never have trouble recognizing a Polygonella.

This shot shows the brown ocreas (cigar bands) at the places where leaves are or were, and the branching oddly spaced between the leaf attachment points. In normal plants bracning happens at the leaf attachment points. (By JB)

Also noteworthy, just above each leaf attachment point a cigar band membrane called an ocrea surrounds the stem.  The ocrea is characteristic of the Polygonaceae Family and turns up also in the big kinfolk:  Sea-Grape and Pigeon-Plum.   In some species., including our Stout Jointweed, the ocrea has long bristles on its top edge.

Faced with the heavenly flora displays of Polygonellas, the question must bas asked, what pollinates those lacey flowers?  Multiple insect species visit, but the interesting one is the Polygonella Bee Perdita polygonellae.  It is a Polygonella specialist, a single insect species dedicated to a genus of plants.  Which came first, the Polygonella or the bee?

White on white, P. robusta this week (by JB)

Kwick Key to the Common Treasure Coast Species

(The English names are inconsistent and messy.)

1. Ocrea with no bristles…2

1. Ocrea with bristles…3

2. Plants essentially leafless when flowering…Slender Wireweed,  Polygonella gracilis

2. Plants with leaves shaped like little canoe paddles…Octoberflower, Polygonella polygama

3.  Leaf blades usually < 1.3 mm wide,  the margins not translucent…Fringed Jointweed, Polygonella ciliata

3. Leaf blades to 2.5 mm wide, the margins translucent…Stout Jointweed, Polygonela robusta