True grasses are plants of the Poaceae family; grass-like plants are often part of other families. Endangered grasses and grass-like plants in Maine include New England Northern reed-grass; smooth whitlow-grass, which has four-petaled white flowers; long-tubercled spike-rush, found in wet, sandy and peaty swamps and shores; sharp-scaled manna-grass; wavy bluegrass, only found at Mount Katahdin; tall beak-rush; Indian grass, found on the prairies in the Great Plains; mountain hairgrass; and yellow-eyed grass, a semi-aquatic plant found in marshes and bogs. Boreal bentgrass, pickering's reed bent-grass and neglected reed-grass are some threatened species.
Ferns are a group of vascular plants that have internal canals for water and sap, but lack seeds or flowers. Among the endangered species of ferns of Maine are the green spleenwort; the aleutian maidenhair fern; the noonwort; and the male fern. Endangered orchids include the ram's-head lady's-slipper, the smallest and rarest lady slipper growing in Maine; the rose-purple showy orchis, growing in Franklin, Kennebec, Oxford and Somerset counties; the giant rattlesnake-plantain; and the white adder's-mouth, which has small greenish-white flowers and short stalks. Small round-leaved orchids are a threatened orchid species growing in Maine.
Endangered aquatic plants in Main include comb-leaved mermaid-weed, which grows in sandy bogs and coastal plains of Cumberland, Hancock and Oxford; and slender pondweed, restricted to alkaline ponds of Aroostook County. Some of the threatened aquatic species include featherfoil; small yellow water crowfoot; spotted pondweed, which has lance-shaped submersed leaves and grows in peaty and muddy acid waters or shores; and pygmy water-lily, growing in Aroostook and Piscataquis counties.
Sedges are plants of the family Cyperaceae, featuring stems with triangular cross-sections. Endangered sedges of Maine include 14 species of the genus Carex, such as the swarthy sedge, awned sedge, bicknell's sedge and the russett sedge. The Carex genus also has three species that are threatened in Maine: the meadow sedge, the prairie sedge and the orono sedge.
Endangered trees and shrubs of Maine include the tundra dwarf birch; the swamp birch; the furbish's lousewort, endemic to the banks of the St. John River; the beach plum, growing in sandy coastal beaches; clammy azalea, which has terminal clusters of four to nine flowers; the Canada buffaloberry; the scarlet oak; the Arctic willow, found in Mount Katahdin; the hoary willow, growing in Aroostook county; and the sandbar willow, a shrub with elongated pointy leaves. Another four species of the genus Salix, which characterizes the willows, are threatened in Maine. The chestnut and the swamp whit oaks are also threatened trees.