A Small Beauty: Purple Milkwort

As we walked the path between the woods and the meadow at the Pole Farm section of Mercer Meadows, Wood Nymphs flitted in and out of the foliage, Monarchs flew by, some mating, and a Clouded Sulphur dipped into the path to lay eggs, the tip of her abdomen touching the leaves of White Clover for a split second each.

Monarch butterflies mating

Wood Nymph

Glancing down, I saw a small group of plants that at first glance looked like a type of clover.

Purple Milkwort (Polygala sanguinea).

But it wasn’t clover. The plants had narrow, alternate leaves, and the tiny flowers were tightly packed into a somewhat flat-topped cylindrical cluster.  It was Purple Milkwort (Polygala sanguinea).

In profile, the outside of the flowers in the cluster (inflorescence) look like overlapping scales, similar to those on a pine cone. These scale-like structures are sepals, the outermost appendage of a flower.  When present, sepals protect the other flower parts as they mature.  In Purple Milkwort, two sepals fuse to form these scale-like outer flower parts, each for a separate flower.

Purple Milkwort (Polygala sanguinea), with unknown insect, probably a beetle, investigating its flowers

Viewed from the top, the inflorescence looks like a single very showy flower.

Purple Milkwort (Polygala sanguinea)

A closer inspection tells a different story. The outermost layers of the display look like white petals dipped in purple, but they are the sepals visible when the flower cluster is viewed in profile.  Moving inward, there are tube-like structures, in luscious shades of yellow, peach and a deep bright pink, reminiscent of popsicle colors.  These tubes are the fused petals of the individual flowers that form this cohesive cluster. At the very center of the inflorescence is a bouquet of buds that have not yet opened.  Together these flowers and buds offer an impressive show.

Purple Milkwort (Polygala sanguinea). The fused petals form a tube, initially yellow, then fading to peach and deep pink.

What explains the different colors of the floral tubes? If you look carefully, the yellow flowers are closest to the center of the display.  They are the most recently in bloom, open for business, the bright yellow actively beckoning pollinators.  The peach flowers have been open longer, and are shutting down.  The deep pink flowers have been in bloom the longest, and are no longer seeking pollinators for themselves.   This kind of color change is usually a plant adaptation to direct pollinators only to the receptive flowers that have not yet been pollinated.  It makes the most efficient use of the pollinator’s efforts from the perspective of both the pollinator and the plant.  While the peach and pink flowers are not beckoning pollinators for themselves, they continue to add to the attractiveness of the overall floral display.

This brightly colored display works! It attracts small to medium sized bees and bee-flies with tongues long enough to reach down the floral tube for a nectar reward.  The photos below show a Sweat Bee (Halictid bee, Augochlorini tribe) exploring the flowers.

Sweat Bee (Halictid bee, Augochlorini tribe) exploring a Purple Milkwort (Polygala sanguinea) inflorescence

Sweat Bee (Halictid bee, Augochlorini tribe) positioning its proboscis for a drink from a Purple Milkwort (Polygala sanguinea) flower

Mmmm, delicious! Sweat Bee (Halictid bee, Augochlorini tribe) drinking nectar from a Purple Milkwort (Polygala sanguinea) flower

Purple Milkwort can be found in the ground cover layer of meadows, prairies, open fields and woods edges from Nova Scotia west to Ontario in Canada, and in much of the eastern two-thirds of the United States, except Florida. It can grow to a height of four to sixteen inches (1-4 dm).  Both the common and scientific names reflect the color of the flowers and the milky sap the plant contains.  The genus, Polygala, is derived from Greek words that mean ‘many or much’ and ‘milk’, referring to the sap.  The species, sanguinea, is derived from a word that means ‘blood’.  Other common names for Purple Milkwort are Blood or Field Milkwort, reflecting its color or habitat.  Although common, it’s not always easy to spot this little beauty.

Follow the camera lens to the Purple Milkwort in the shadows in the lower left of the photo.

Resources

Mauseth, James D. Botany An Introduction to Plant Biology.  2014.

Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania.  2007

Stearn, William T. Stearn’s Dictionary of Plant Names.  1996

Wilson, Joseph S.; Carril, Olivia Messinger. The Bees in Your Backyard. 2016.

Flora of Wisconsin

Illinois Wildflowers

Minnesota Wildflowers

USDA NRCS Plants Database

 

 

13 thoughts on “A Small Beauty: Purple Milkwort

  1. Thank you, Mary Ann for your photos of the purple milkwort. It has so much more meaning to me now that I have seen you at work. Jeff Worthington caught an authentic shot of our own Citizen scientist/artist. Your posts always make my day.

  2. Love the photos. I’m getting a post ready that’s about colour matching in nature and wondered if you’d let me use one of the sweat bee photos. I’m using 8 or 9 photos all up. I’d clearly link back to your post and your blog home. Is that ok with you?

  3. Pingback: Sweat Bee and Purple Milkwort – Exploring Colour

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