Smooth slender crabgrass, a plant known to exist only at Rock Rimmon Park in Manchester, has been officially declared globally extinct, the N.H. Natural Heritage Bureau announced Wednesday.

This is the first documented plant extinction ever in New Hampshire, but probably won’t be the last.

This species (Digitaria filiformis var. laeviglumis) existed only in 140-acre Rock Rimmon Park, which rises 350 feet above the Merrimack River. The park is a surprising hotbed of plant diversity, partly because of its geology that led to different levels of soil acidity, supporting at least 10 vascular plant species at risk of extinction.

First seen and named here in 1899, smooth slender crabgrass was last officially collected in 1931. It has not been found since then despite 25 botanical surveys, including 11 specifically looking for it.

New Hampshire has about 1,400 known native plant species and about 400 of them are being tracked as endangered or threatened. There have, however, been a few successes such as the northeastern bulrush, a sedge found in New Hampshire that was recently taken off the federal endangered species list as its population rebounded.

The loss of one type of grass that looks almost exactly like many other types of grass growing amid the boulders at one city park may not seem important, but a gathering of botanists and ecologists from state agencies and environmental groups for a tour of Rock Rimmon last October, as reported in the Monitor, said that’s a mistaken belief.

“It’s hard to get people as excited about crabgrass as rhinos, but it’s just as important,” said Sean O’Brien, leader of NatureServe, an organization that supports biodiversity conservation efforts by groups and governments. O’Brien cited a famous 1991 essay by scientist Paul Erlich that compared species to rivets on an airplane. “You can remove a rivet and another rivet and it won’t do anything but if you remove the wrong one, the wing will fall off,” he said. “We don’t know which (species) is that rivet.”

This is the fifth plant in New England ever declared globally extinct.

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