The rarest of New Hampshire plant species — smooth-slender crabgrass known to exist only in Manchester — is officially extinct, the New Hampshire Natural Heritage Bureau announced Wednesday.
The Heritage Bureau said that recently concluded scientific studies had ruled out the possibility that look-alike plants in Mexico and Venezuela were identical to the New Hampshire plant, Digitaria laeviglumis.
The plant’s one and only location in the world was Rock Rimmon — the prominent rock outcropping on the West Side of Manchester that is part training site for rock climbers, part nature walk for outdoor lovers, part breeding ground for rare plants and part party spot for bored youth.
Smooth-slender crabgrass is not the same plant as the weed that plagues most lawns in the city. That common crabgrass is actually not native to North America.
Smooth-slender crabgrass was first collected by botanist Frank Batchelder in 1901. It was last collected in 1931. Since then, scientists have engaged in at least 24 botanical surveys of Rock Rimmon in search of the plant. All have been unsuccessful.
The Heritage Bureau said there are likely several reasons for the demise of the species — heavy recreational use, severe soil erosion on the summit, competition from common crabgrass species and its popularity among scientists.
“The high number of smooth-slender crabgrass collections from 1931, made by botanists as a way to formally document the species, may have inadvertently contributed to its demise,” said Bill Nichols, senior ecologist and state botanist at the state Natural Heritage Bureau.
The plant extinction is the first documented in New Hampshire and only the fifth in New England since European settlement.
Rock Rimmon is located on the West Side near the park that bears its name and Northwest Elementary School.
The top of the rock offers views of the city and is the unofficial gateway to the massive Black Acres, an unbuilt section of the city that features powerline rights of way, woods, scrub and sandpits.
“A lot of people recreate out there,” said Manchester fire Lt. Scott Brassard, who is assigned to the Amory Street fire station. He said the department gets medical calls, such as injured hikers and overdoses.
The fire department also gets called out for brush fires at Rock Rimmon. Occasionally, climbers have gotten stuck climbing the rock face. Families sometimes hike up for the view, Brassard said.
“I remember going up there when I was a kid,” he said.
The Heritage Bureau said Rock Rimmon is a botanical hot spot. Records dating back to 1899 document 10 state endangered or threatened species. Five, including smooth-slender crabgrass, are no longer at Rock Rimmon because of human-related activities.
Mark Gomez, the chief of city parks, said the rock face and top are city property. He said the city maintains the trails to the top in a passive sense by addressing erosion and allowing volunteer litter cleanup crews.
He said if more money were available, the city might be able to more actively maintain and promote the area.