Drawing the Line

With permission granted to collect just a few more samples, I went back to the iris sites and got two capsules. Each one appeared to be ripe. Took them home, opened them up, photographed them…

And damn if I still haven’t reached a conclusion.

According to the Flora of North America, Iris virginica has

Seeds in 2 rows per locule, pale brown, usually D-shaped, 5–8 mm, pitted, corky. 2n = 70, 72.

while Iris versicolor has

Seeds dark brown, D-shaped, 5–8 mm, shiny, thin, hard, regularly pebbled, not corky. 2n = 108.

How would you describe these seeds?

Once again I sought expert advice, this time from the Species Iris Group of North America and an iris-specific internet forum. One kind gentleman wrote to me:

Elizabeth Miller, please see the paper attached below. Iris virginica is 2N = 70 Iris versicolor is 2N = 108, it is an allopolyploid stable hybrid of Iris virginica and Iris setosa (2N = 38) which occurred post glaciation after the Laurentide Ice Sheet shifted a population (dramatically) from Western North America all the way across to the East, into the range of Iris virginica. Since you have a permit for collection, you may wish to contact your nearest university with a Hort program and see if they can do an analysis. In general from a phenotypic perspective Iris versicolor has short standards, which it inherits from Iris setosa, which has bristle like almost invisible standards. But Iris virginica phenotypes are variable and some occasionally have a shorter or rounder standard. So it is best, and most accurate, to go with a chromosome analysis:

[Parental Origin and Genome Evolution in the Allopolyploid Iris versicolor]

I was also pointed to the classic article “The Problem of Species in the Northern Blue Flags, Iris versicolor L. and Iris virginica L.”, by Edgar Anderson, originally published in Annals of the Missouri Botanical Garden [Vol. 15, #3, Sept. 1928].

The article was fascinating, and I’ve been struggling to come up with a way to briefly summarize it while doing justice to the detail. If you’re interested in such things, it’s worth getting a (free) jstor account.

After introductory remarks and descriptions of the species, the author presents a chart of “Comparative Morphology”, followed by some interesting observations:

Wherever either species was studied, the individual plants which went to make up a colony were found to vary strikingly among themselves. They varied in every conceivable characteristic, both vegetative and floral… The flowers varied in size and form, in color and color pattern, in number and arrangement, in texture…

…It is thus apparent at the outset that no biometric method of distinguishing the two species can be a simple matter.

That made me feel better about my own failed attempts. It also made me wonder if I wasn’t right in thinking that the lumpers should have won this round. But earlier in the paper, Anderson writes

It has been found that what commonly passes for Iris versicolor L. is made up of two species… the species are wholly distinct and crosses between them are partially sterile.

So I kept reading, only to discover that after detailed analysis of numerous specimens, Anderson discards mathematical models and comes up with a fascinating method of comparing specimens by creating ideographs based on groups of characteristics. After comparing ideographs, Anderson concludes

In marked contrast to the variation between individuals is the general resemblance between colonies of the same species.


Above all, when the ideographs are considered as a whole, the two species remain completely and absolutely distinct. In spite of a wide range of variation in separate characteristics, when the combination as a whole is studied it is found to be strikingly constant. Iris versicolor remains always and unmistakably Iris versicolor, and Iris virginica remains always and unmistakably Iris virginica. There is not the slightest tendency to one species to merge into the other.

So where does all this leave me? I can’t create the ideographs without access to a large number of specimens – quite possibly more than either stand of irises affords. Which leaves chromosome analysis.

And that’s where I draw the line. Even though a botanist friend has promised use of her microscope so I can do it the “old-school way”, should I be able to collect samples of root tissue.

Those Damned Irises

On June 29, with my collecting permit about to expire, I went one more time to visit those two stands of irises near the Marsden Tract*, and collected two more seed capsules. Took ’em home, opened ’em up, photographed, measured, examined with hand lens, etc.

And got nowhere. The seeds just weren’t ripe enough.

My gut feeling is that stand 1 is Iris virginica and stand 2 is Iris versicolor, based on the observed characteristics. The former is on the state DNR watchlist (S3), and there are records of it in Montgomery County, so this is not too far-fetched.

But I like proof, and I haven’t proven anything, except that I’m a little nuts, so I am going to conclude that both stands are probably Iris versicolor, because it’s the more common species.

However… this ain’t over yet.

*see posts from mid May into June


The Iris ID Odyssey Continues

It worked. With a friend’s help and introduction I was able to get a collecting permit. Unfortunately by that time Stand #1 had finished flowering, but I did collect one flower from Stand #2, and one capsule from each stand.

Here’s a summary of my notes. (Refer to the last four posts from this past May for details, particularly the one from May 27.)

Stand #1
No flowers remaining. Most flowering stems appear to have been cropped about halfway up. One untouched stem was flopped over [I. virginica]; the other (cropped) stems were upright [I. versicolor or I. virginica var. shrevei]. The collected capsule was conspicuously beaked [I. versicolor], measured 70mm long by 13mm wide, and was broadly triangular in cross section.The spathe associated with this capsule was dry and papery [I. versicolor]. The seeds were underripe: still green, with shiny outsides that did not appear to be corky [I. versicolor] and may or may not have been pitted.

Stand #1: capsule with spathe

Stand #1: seeds







Stand #2
The collected flower had sepals measuring 55mm, 55mm, and 56mm long, and the corresponding petals measured 38mm, 38mm, and 39mm long, or 2/3 the length of the sepals [either species], The style arms appeared to have auricles at the bases [I. virginica]. The collected capsule measured 70mm long by 11mm wide and was not beaked [I. virginica by implication?]. The associated spathe was slightly dry and papery [I. versicolor]. Other observed (not collected) capsules were somewhat or not at all beaked, and their associated spathes appeared to be drying and papery [I. versicolor]. The seeds were underripe: still green, with shiny outsides that did not appear to be corky [I. versicolor] and may or may not have been pitted.

Stand #2: style arm, petal, sepal

Stand #2: two style arms

Stand #2: capsule

Stand #2: seeds



















from Flora of North America:

Iris versicolor
…Capsules often persistent over winter, ovoid to oblong-ellipsoid, conspicuously beaked, obtusely triangular in cross section, 1.5–6 cm, tardily dehiscent. Seeds dark brown, D-shaped, 5–8 mm, shiny, thin, hard, regularly pebbled, not corky.

Iris virginica
…Capsules ovoid, ellipsoid, or long-cylindric, trigonal or polygonal in cross section, 3–6 × 1–2 cm. Seeds in 2 rows per locule, pale brown, usually D-shaped, 5–8 mm, pitted, corky….Plants of Iris virginica from the southeastern and south-central states having stems 2–3-branched and seldom falling to the ground after flowering, and with capsules long-cylindric have been recognized as var. shrevei.

So, I’m still not sure. Just looking at the flowers (and later, the pictures), I want to say that Stand #1 is I. virginica var. shrevei, and Stand #2 is I. versicolor. My instinct says they have to be I. versicolor (“go with the more commonly occurring species” is my rule). But I’m trying to be methodical about this.

obligatory flower pic

I spent some time Wednesday morning in the Brookside Gardens library, reading about both these species in several different books, and taking lots of notes. If you’re truly interested in irises, keep reading…




from The World of Irises, Bee Wharburton, Editor, Melba Hamblen, Assistant Editor; The American Iris Society Wichita, Kansas 1978:

Iris Virginica and Versicolor
These two members of the Laevigatae are similar and have long been confused; they share the common name “Great Blue Flag.” They can ordinarily be separated in that virginica is overall a more slender plant, with full-size standards quite as long as the falls, while those of versicolor are shorter and rather bluntish. Seeds of virginica have a dull, corky look, while seedcoats of versicolor are brittle, thin, and shiny. Both are absolutely at home in shallow water or wet marsh conditions… [p. 304]

Iris versicolor has the highest chromosome number known in the genus iris [sic], 2n=108. Edgar Anderson (1936) demonstrated that it originated as an amphidiploid hybrid of I. virginica (2n=70) and I. setosa var. interior (2n=38) in preglacial or interglacial time. It is essentially a tetraploid hybrid with exceptional fertility and vigor. This is a famous case of the origin of a new species by hybridization. [p. 305]


from The World of Iridaceae, Clive Innes; Holly Gate International Ltd., 1985:

I. versicolor
Plants 20-80cm. tall. Leaves forming clumps, erect or curved, 1-2cm. wide, stained purplish at base. Stem branched, several-flowered, stout and erect. Flowers 6-8cm. diam., varying shades of purple to lavender veined yellow, green or white. Falls spreading, 5-9cm. long, the blade ovate, crestless, purple or violet veined deeper, haft broad, greenish yellow veined purplish. Standards erect, narrow, spathulate, shorter than falls, purple veined deeper or whitish, purple veined towards narrow base. Style branches lilac with whitish margins, broadly linear. Anthers blue. Flowering May to July. From Canada (eastern areas) to USA (southern states on east) on high ground and low, in moist marshy areas — very widespread. [p. 243]

I. virginica
Plans 30-100cm. tall. Leaves soft, green, buff to pale brownish at bases, 1-3cm. wide. Stem simple, rarely branched, arching, becoming almost pendent after flowering. Perianth tube very short, scarcely more than 1cm. long. Flowers 1-4 to a stem, 6-8cm. diam., lavender, blue, bluish-purple, violet — a white form is also known. Falls spreading, the blade oblong or ovate, 3-4cm. wide, blue with central yellow blotch, somewhat hairy, the haft yellowish-orange streaked. Standards erect, obovate or spathulate, 5-6cm. long (slightly longer than falls), 1-2.5cm. wide, wavy-edged or notched, purple. Anthers white or yellow. Flowering May to July. From USA (Louisiana, Virginia, Florida and east Texas in marshy, swampy areas). [p. 244]


from The Iris, Brian Mathew; Universe Books, 1981:

I. versicolor Linn. This robust clump-forming plant has stout creeping rhizomes giving rise to erect or arching leaves about 1-2cm wide and stems 20-180cm in height, equalling or slightly exceeding the leaves. The branching flower stems carry several flowers, each about 6-8cm in diameter and usually some shade of violet, blue-purple, reddish-purple, lavender, or dull slatey-purple. The falls are widely spreading and often have a greenish-yellow blotch at the center of the ovate blade, surrounded by a white area variegated with purple veins, this continuing down the haft. … I. versicolor is a very widespread plant in eastern North America from eastern Canada southwards to Texas. It grows n marshes, swamps, wet meadows and on lake shores and flowers in May, June or July. [p. 104]

I. virginica Linn. The Southern Blue Flag. This is sometimes considered by botanists to be inseparable from I. versicolor. [emphasis mine] I am not familiar with either in the wild and would not care to judge. Currently it is treated as a separate species by several American Floras. As its common name suggests, it has bluer flowers an is confined to a more southerly part of the United States. The height varies, 30-100cm, and the stems are often arching, falling to the ground in the fruiting stage. The leaves, 1-3cm wide, are soft and flopping over at the tips. In typical I. virginica there may be one short branch on the stem but usually it is simple. The one to four flowers are 6-8cm in diameter with spreading falls of blue, violet, lilac, lavender, or occasionally pinkish-lavender. In the centre of the 3-4cm wide, oblong or obovate blade there is a prominent yellow hairy patch which helps to distinguish I. virginica from I. versicolor. The standards are erect and smaller, usually narrowly obovate or spathulate in shape… I. virginica grows in marshes, damp pinewoods, ditches and wet grassy places in Florida and eastern Texas northwards to south-eastern Virginia. It flowers from May to July…. Although very similar in appearance to the latter [I. versicolor] it may be recognized by the flower colour which is usually in the bluer end of the spectrum (reddish-purple in I. versicolor) and by the yellow hairy patch on the falls. [p.105]

Note the sentence in bold above: some botanists consider the two species inseparable. Lumpers and splitters… Can I just call it an iris and be done?

But that’s not how I am. My permit is valid until June 30 and allows me to collect two more capsules, so I will be checking the condition of these plants a few more times, and when the capsules appear ripe, or on June 30, whichever comes first, I’ll be going through all this again. The resulting post will be shorter, though.

A Beautiful, Useful Pest


yellow flag iris, pale yellow iris
Iris pseudacorus


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…”



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