Partridge Peas and Ambivalent Bees

Partridge Peas

Chamaecrista fasciculata

Caesalpiniaceae

Okeeheelee Nature Center is in Okeeheelee Park near the Florida Turnpike in West Palm Beach.  CLICK   The 2.5 miles of trails criss-cross through dry pine woods interspersed with ponds and marshy areas, a pleasing natural reserve in the middle of our urban area.  So John and I went there today with cameras in hand.

Okeeheelee

Each time and place has one standout species.  Yesterday it was Partridge Pea in splendid flower over the river and through the woods.   Looks misleadingly a little like a fern, well, sorta.  More like Sensitive Plant but no, and not that sensitive.  Resembles a Cassia plenty, and has historically been classified as one.  A little weedy, Partridge Pea is adaptable and variable, basically an annual or slightly woody subshrub with ferny compound leaves, butter-yellow flowers, and flat pea pod fruits.  It’s everywhere, especially dryish disturbed sites, but sometimes where it is moist, in the sun or under the understory—-you can’t miss it.  Recently burned places are good places to look.   The species ranges from Florida across most of eastern and central North America.

Partridge Pea (by JB)

This is one of many local species equipped with foliar nectaries to feed ants.  Look on the stalks of those compound leaves for a little nectar gland on each leaf.  The plant feeds ants, and the ants provide Security Services.  Lots of plants and ants symbiose; on the same outing we saw similar glands on the leaf stalks on Bracken Fern, on a Senna at the Visitor Center, on Caesarweed, and on Cocoplum.

The gland is near the base of the leaf-stalk (JB)

The flowers are open just one day.  Pollination is exclusively by bees, and then only those whose “buzz” has the correct frequency to cause the pollen to puff out of pores at the anther tips.  The stamens (pollen-producing organs) are of two lengths, the shorter ones feeding pollen to the bee, and the longer ones depositing pollen onto it.

This photo (by JB) shows the short stamens and the longer ones.  The single structure angled to the right is the (female) style.  Note how the style is angled to the right, and read on.

 

Researchers examining Chamaecrista using electron microscopes have found the stigma (pollen-receiving organ) to be in a small cavity covered in hairs, and to require the “right” buzz for pollen reception.   Preliminary indications (or conjectures) are of a liquid in the cavity that “comes forth” when buzzed properly, able then to snatch the pollen in glue.  (This glue resembles the pollination droplet characteristic of “primitive” seed plants.) The wrong bug carrying the wrong pollen isn’t going to contaminate these very exclusive flowers.

Oddly, buzz flowers tend to have the flowers in an alternating “mirror image” left-right-oriented sequence.  Looking at the flower face-on, the styles (and possibly stamens) are either bent to the left or right.  This link CLICK shows the right-face, left-face, right-face etc. alternation of the skewed flowers.  Check also the link in the notes below.

The alternation pattern is called enantiostyly (ee-NANT-ee-oh-style-ee) and is known in varied unrelated plants.  In at least some species, the left-skew, right-skew pattern is under the control of a single gene, functioning as a toggle.  What enantiostyly is all about is a little controversial, and possibly more than one benefit, and is a matter of current research.   For a short explanation, pollen placement and removal on the bee is precise, and the bilateral application increases efficiency by addressing both sides of the bee.

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Notes:  Another nice link showing the left- right- skewed flowers: CLICK

Even the opening pods have a mirror-image thing going on (JB).