Wednesday, May 8, 2013

A tale of two flowers - one native, one alien

Our local newspaper offers a feature where they publish comments from the community on a regular basis.  Most of the comments are political, or complaints about something or someone.  I wait for one comment every year, someone will call in to exclaim how beautiful the Wild Phlox is in Mill Pond Park and how it is just covering the woods!

Woods covered with "Wild Phlox"

Only one problem.  It's not Wild Phlox.

It's Dame's Rocket (Hesperis matronalis).
Dame's Rocket - Note four petals on flowers and alternate leaves

Dame's Rocket is indeed a beautiful flower, but it is not a native plant to Mid-Michigan or even North America.  It is a native of Eurasia.  It is widely cultivated as a garden plant and easily escapes cultivation.  As an alien species that spreads easily it can be classified as an invasive species.  It is on noxious weed or banned plant lists in three states (Colorado, Connecticut, Massachusetts) because of its noxious habits.

Like other members of the Mustard (Brassicaceae) family -which includes other noxious weeds such as Black Mustard (Brassica nigra) and Garlic Mustard (Alliaria petiolata) - Dame's Rocket can be identified by the arrangement of its petal and flowers.  The flowers are arranged alternately along the stem and the flowers contain four petals in a cross-like formation.  The Brassicaceae used to be named the Cruciferae "cross-bearing" for this petal arrangement. 

Close-up of Dame's Rocket flowers - note the cross-like arrangement of the four petals

Dame's Rocket is a very showy plant.  Individual plant may grow up to 3 foot tall  and can be covered with dozens of white, blue, or lavender  flowers.  Because it has such prominent blooms and a long bloom period, it has long been a favorite among gardeners.  That is why it has escaped so easily into the wild - it can be found in forty-one states and eleven Canadian provinces and territories.

So if this spectacular show in our local woodlands every May to August is actually an invasive species, do we have any native phlox in Mid-Michigan?

Yes!  The Wild Blue Phlox (Phlox divaricata) grows in forests and floodplains throughout the eastern United States and Canada.  In Mid-Michigan it can easily be found in moist deciduous forests and floodplain forests, and along the margins of deciduous swamps.

It is easily distinguishable from the non-native Dame's Rocket by its leaf and flower arrangement.  The leaves are arranged in opposite pairs along the stem.  Flowers always have five petals.  The petals are fused into a tube at the base of the flower, but spread out into wide lobes.

Wild Blue Phlox is not as spectacular as Dame's Rocket.  It only grows to a height of 6 to 20 inches tall.  It blooms before the Dame's Rocket (April to early June in Mid-Michigan) and is a late Spring wildflower compared to the summer blooming Dame's Rocket.  It has a more delicate beauty that can be overlooked in favor of the showy, but alien Dame's Rocket.

It is wonderful that people celebrate the beautiful flowers blooming in the woods.  Just make sure that you are celebrating the right plants for the right reasons.  Sometimes the showiest plants are those that are out of place.

Basic Information

Dame’s Rocket 
Hesperis matronalis

Size:  1-3’ tall

Habitat:  open woodlands, thickets, roadsides, fields

Flower Color:  purple, blue, or white

Bloom Time:  May – August

Non-native Plant

Wild Blue Phlox 
Phlox divaricata

Height:  10-20” tall

Habitat:  woodlands, floodplains, wooded dunes

Flower Color:  pale blue 
Bloom Time:  April – early June

Native Plant

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