Getting Madders

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Houstonia caerulea (azure bluet)

If you go botanizing during growing season, year after year, you notice trends. For example, there’s almost always something in the Asteraceae (daisy family) blooming, but the family really gets going in high summer and into autumn. Plants in the Violaceae (violet family) bloom in early spring and are done by the time the earliest Lamiaceae (mint family) start. And so on.

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Cephalanthus occidentalis (buttonbush)

This is the time of year for the Rubiaceae, or madder family. Worldwide, it is the fourth largest flowering plant family in terms of number of species (Asteraceae, Orchidaceae (orchid family), and Fabaceae (pea family) are first, second, and third). Depending on which authority you consult, there are about 13,500 species in more than 600 genera.

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Galium concinnum (shining bedstraw); the flowers are about 3/16″ wide

The Rubiaceae is a cosmopolitan family, with species found worldwide except in the polar regions, but most are in the tropics or subtropics. The plants can be trees, shrubs, lianas, or herbs. Some are well-known garden ornamentals (pentas, ixora, gardenia), and some are economically important, producing dyes (like madder), or drugs (like quinine), or beverages (coffee!).

Here in North America, Rubiaceae ranks 18th, with 264 native species. (Asteraceae is first, Fabaceae second, and Orchidaceae ranks 13th.)

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Diodia virginiana (Virginia buttonweed)

In Maryland, Rubiaceae is tied with Onagraceae for 13th place, with 39 species. (Asteraceae is first, Fabaceae second, and Orchidaceae is tied with Plantaginaceae for 9th place.)  I gleaned this information from the Maryland Biodiversity Project but did not weed out the aliens, so if you count only natives the rank may change. But you get the idea.

Geez, this is starting to read like baseball stats.

Anyway, the Maryland species fall into eight genera:

  • Cephalanthus (one species, C. occidentalis, aka buttonbush, found almost statewide)
  • Diodia (two species, D. teres and D. virginiana, both found primarily in the Coastal Plain and Piedmont)
  • Gallium (as many as 24 species depending on taxonomy; distribution varies)
  • Houstonia (five species; see previous post)
  • Mitchella (one species, M. repens, aka partridgeberry, found statewide except Washington County)
  • Oldenlandia (one species, O. uniflora, aka clustered mille-grains; coastal plain)
  • Sherardia (one species, O. arvensis, aka field madder, alien found in the coastal plain)
  • Spermacoce (one species, S. glabra, aka smooth false buttonweed, listed S1/endangered, found in Montgomery County)
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Houstonia purpurea (purple bluet)

Looking at just the sampling of species here in Maryland, you can see traits that characterize the family: flowers consist of four petals, often pointed, partly fused into a tube; there are two leaves or more per node on the stem (opposite or whorled arrangement), the leaves usually entire, and often there are stipules. Most are herbaceous, except partridgeberry, which hugs the ground and never gets more than an inch tall yet has a woody stem, and buttonbush, which is a shrub. I should note, though, that there are many exceptions to these traits in the worldwide accounting of species.

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Mitchella repens (partridgeberry)

 

Variations on a Theme: Venus’ Pride and Longleaf Bluets

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Houstonia species, Rubiaceae

Nationwide there are 18 species of Houstonia, only five of which are found in Maryland; one of those one is found only in Garret County. In the Piedmont, two of these species (azure bluet and Venus’ pride) are rather widespread, and two (longleaf bluet and small bluet) not so much.

Last June I thought I’d found both Venus’s pride and longleaf bluet along the C&O Canal near the Marsden Tract. This year, when I went in search of them I found only Venus’ pride, but I did find longleaf bluet on Sugarloaf Mountain. Here’s a little primer about the two. Their flowers are almost identical; it’s the leaves that differentiate them.

I took measurements of only a few plants, and each patch of plants contained only a few individuals, so consider this casual observation rather than proper science.

A note about color: these flowers were all vaguely purple… in the right light. In some of these photos they’ll look white, which is pretty much how they appear in strong sunlight. In shade the purple, while faint, is more apparent. Despite the moniker “bluet”, they never seem blue.

There’s a little glossary at the end.


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Houstonia longifolia
common names: long-leaved bluet, longleaf summer bluet

  • perianth about 1/4″ long
  • corolla about 3/16″ wide
  • plant height estimated 4-6″
  • leaves opposite, 1/2′ to 3/4′ long, linear shape, one-nerved, margins entire, stipules present

H. longifolia is present in Maryland in parts of the Piedmont and one section of the Coastal Plain, but is found mostly in the Blue Ridge and Ridge and Valley physiographic provinces. BONAP shows it as rare where present in Maryland, but it’s not on the state DNR list of rare, threatened, and endangered plants.

Taxonomic note: MD DNR lists another species, H. tenuifolia, as S1/endangered. However that species is not recognized by ITIS, which considers is a synonym for H. longifolia. What that means for conservation efforts I have no idea.

H. longifolia grows mostly in the Appalachians and Ozarks, and in parts of the Upper Midwest. It’s endangered in Connecticut and Massachusetts, special concern in Maine, and historical in Rhode Island.

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Houstonia purpurea
common names: purple bluet, Venus’ pride, woodland bluet, large bluet

  • perianth about 3/8″ long
  • corolla about 3/16″ wide
  • plant height estimated 4-6″
  • leaves opposite, 1″‘ long, oval shape, three-nerved, margins entire but ciliate, stipules present

H. purpurea is present in the Maryland Piedmont and parts of Coastal Plain. Per BONAP, it ranges through the Appalachians, the Ozarks, and much of the South, but not the Upper Midwest.

ITIS lists three varieties, two of which are endangered in New York; the third is endangered in North Carolina and Tennessee and is also on the federal endangered species list.

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perianth: the sepals and petals of a flower, collectively
corolla: the petals of a flower
ciliate: fringed with hairs
stipule: small, leaf-like growth where leaf meets stem

sources:
BONAP the Biota of North America Program
ITIS the Integrated Taxonomic Information System
Maryland Biodiversity Project