A Beautiful, Useful Pest

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yellow flag iris, pale yellow iris
Iris pseudacorus
Iridaceae

 

In motor racing a yellow flag shown to competitors is a warning: there’s a potential hazard on or near the racing surface, something that could cause a serious problem.

“Yellow flag” is a good name, then, for this particular iris. Native to North Africa and Europe, it was introduced to the US and Canada in the early 1900s as a garden ornamental. As early as 1911, it was found in the wild in Newfoundland, and it took only a few decades to establish itself as a serious wetland pest, capable of outcompeting all other plants to form dense monocultural stands.

This is not merely an aesthetic problem for people like me who enjoy the beauty of native flora. Loss of floral diversity leads directly to the loss of faunal diversity, from insects to mammals. The ripple effects of a changing hydrology can be enormous:

The clonal nature of I. pseudacorus causes it to form dense stands and thick, submerged rhizome mats (Idaho Invasives 2007, Lui et al. 2010) that can prevent the germination and growth of native species (sedges, rushes, etc.) and eventually displace them entirely (Lui et al. 2010, MNDNR 2012, Noxious Weed Control Program 2009, ODA 2012). This vegetative growth can also trap sediment, raise local elevation of the ecosystem, and alter wetland hydrology (Noxious Weed Control Program 2009, Sarver et al. 2008). Populations of yellow iris create a positive feedback loop: once established, the roots trap sediment, which enables growth of new seedlings, which in turn trap more sediment (Jacobs et al. 2011). This increase in sedimentation also creates new habitat for shrubs and trees, thereby altering it to a drier ecosystem (Lui et al. 2010, Sarver et al. 2008). This alteration reduces the food supply and nesting habitat of many fish and waterfowl that depend on wetlands (Noxious Weed Control Program 2009, ODA 2012).*

Like many invasive species, yellow flag iris is highly adaptable to a variety of growing conditions. It prefers to grow in shallow water or wet soils, but once established it is surprisingly tolerant of lower moisture levels. It also tolerates low oxygen levels, high organics levels, and it will grow in a wide pH range, from highly acidic to slightly basic.

Despite all this bad news, if controlled yellow flag iris can be useful. It has been shown to significantly reduce levels of pathogens, including E. coli and Salmonella. It is known to be able to remove heavy metals from wastewater and has been used in sewage treatment systems in the Czech Republic and China.

It’s a stunningly showy plant, a perennial that stands up to five feet tall with dark green foliage and bright yellow blossoms. It’s now blooming in several parts of the recently de-watered parts of the C&O Canal near Carderock. Found in most of the US and Canada (except for 13 states and provinces), it’s reported as invasive in 12 states, including Maryland (where it’s been found in eight counties) and is listed as prohibited or noxious in six states.

Strangely despite the obvious problems it is still recommended by Missouri Botanical Garden because it’s easy to grow in problem (that is, wet) areas of the yard and has pretty flowers, but they also note “yellow flag should not be planted along streams or ponds or lakes where it can spread into natural waterways…”

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Sources:

USDA Natural Resources Conservation Service
Missouri Botanical Garden
Maryland Biodiversity Project
University of Florida, Institute of Food and Agricultural Services
*Great Lakes Aquatic Nonindigenous Species Information System

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

Venus’ Looking Glass

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Triodanis perfoliata
Campanulaceae

This beautiful little flower belongs to an annual plant that’s found all over the continental US (except Nevada), and parts of Mexico and Canada, and is considered weedy.

The plant consists of a single stem about 12 inches tall, sometimes taller, usually a little shorter, whose leaves clasp most of the way around, so that the stem appears to be piercing them. The flowers are found in the leaf axils. Only the upper ones open; the lower ones are self-pollinating.

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I find it in the Potomac Gorge in dry, rocky areas, most often growing right up against a big rock.

The genus Triodanis has only five species. Of these, two are found only in Texas, and two others are found through parts on the Midwest.

Triodanis means three toothed, and may refer to either the three-lobed calyces on the lower stem flowers*, or the fact that the seed capsules open into three parts**.

 

*The Lady Bird Johnson Wildflower Center
** Illinois Wildflowers website

Just Not a Whole Lot Going On

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hairy skullcap
Scutelleria elliptica
Lamiaceae

 

It’s not like me to go for two weeks without posting, but I just haven’t gotten out as much this year. And the times I have gotten out, I’m not seeing much.

On June 6 I hiked about two miles around Carderock. I found a few rather wan-looking blossoms on partridgeberry plants, a single hairy skullcap (in an area where there should have been a dozen or more), some shining bedstraw, and a few blue-eyed grass. A patch of Culver’s root I discovered a month ago appears to have been browsed by deer (bastards). Ramps are in bud. Honewort is blooming, but you really have to be a plant geek to find honewort interesting.

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longleaf bluets
Houstonia longifolia
Rubiaceae

 

On June 7 I hiked about three miles on Sugarloaf Mountain, and found one small patch of longleaf bluets blooming. The mountain laurel are still going, though past their peak (they are all done at Carderock). Other than those and some fleabanes, I saw nothing else blooming, though there was an inch-tall spike starting on a downy rattlesnake plantain.

Looking at notes I’ve made over the past few years, I realize there is a bit of a lull from late May to mid June. But this is pretty slim pickings. I hope to get back to the Carderock area today to look for both purple bluets and longleaf bluets, though it may be too early for them.