Do you remember when I waded through botanical terminology to identify my wild rose? Well, I’ve been at it again. Earlier this week, a pretty lilac-blue flower along the side of the road caught my eye, and I wanted to know what it was.

It was pretty enough to be a garden plant, but I couldn’t remember which plant it reminded me of. A friend suggested it could be brown knapweed (Centaurea jacea). I searched on GoBotany, my favorite wild plant identification tool for northeast North America, and thought that might be it.

But wait a minute!

In the sidebar, it says that brown knapweed can be confused with short-fringed knapweed (Centaurea nigrescens) and black knapweed (Centaurea nigra). To tell them apart, you have to observe the appearance of the involucral bracts on the plant in question.

What the heck is an involucral bract?

Involucral bract on centaurea
The key to distinguishing between three species of Centaurea is the appearance of the involucral bract, or phyllary.

Oh. my. word. Really?
Yes, really. The only way to tell them apart is by looking at those little scale-like things on the base of the flower.

centaurea involucral bract closeup
Here, have a closer look. (Click to enlarge)

How to distinguish between the three species

According to GoBotany, these are the distinguishing features of similar knapweed species found in New England:
Centaurea jacea – apical appendage of involucral bracts light brown to brown, those of the middle and outer series irregularly lacerate, those of the inner series often bifid
Centaurea nigrescens – apical appendage of involucral bracts brown to black, those of the middle and outer series regularly pectinate-fringed, usually none of them bifid
Centaurea nigra – apical appendage of involucral bracts longer than 2 mm, the larger ones mostly 4–6 mm long, with 7–15 fringe segments on each margin, and outer flowers of capitulum not enlarged

There, does that clear it up for you? No? Me, neither.

But it did make me realize I needed a magnifying glass to pay attention to these small differences. I don’t keep a magnifying glass at my desk, but we happen to have a pair of tweezers with a magnifying glass attached, and that was sufficient. I looked at the flower I had picked and noticed that the scales had really long–er, fringes–on them. Could those be the “apical appendages” that are “mostly 4-6mm long, with 7-15 fringe segments on each margin?” By jove, I think they are!

Even though I couldn’t…