The Tick Trefoils are all perennial herbs, often with stout roots, erect, ascending or trailing stems and three-foliolate leaves. The flowers are usually rather small, purplish in terminal or axillary, compound or simple racemes or panicles. Calyx two-lipped, the upper lip two-toothed, the lower lip with three acute or attenuate teeth. Stamens monadelphous or diadelphous (nine and one); anthers all alike. Fruit (loment) flat, sessile or stalked with several joints which are easily separable at maturity.

A large genus of plants with about sixteen representatives in New York State. The following key is given as an aid in placing the various species not fully described and illustrated here.

Loment not constricted above, deeply constricted below, long-stalked; leaflets broad Panicle terminal on the leafy stem

Leaves crowded at the base of the panicle................M. grandiflora

Leaves scattered along the stem..........................M. pauciflora

Panicle arising from the base of the plant, its stalk usually leafless................

M. nudiflora Loment constricted on both margins, more deeply below than above Stems trailing or reclining

Leaflets orbicular, 1 to 2 inches long and pubescent.........M. michauxii

Leaflets ovate or oval, dull green............................M. glabella

Stems erect or ascending

Leaves sessile or nearly so; leaflets linear or lanceolate.....M. sessi 1 i f o 1 i a

Leaves petioled

Joints of the loment notably longer than broad

Leaflets obtuse, yellowish green, rough-pubescent.. . . M. canescens

Leaflets long-acuminate..........................M. bracteosa

Joints of the loment little longer than broad Loment distinctly long-stalked in the calyx

Plants glabrous or nearly so (except varieties of M. paniculata)

Leaflets lanceolate or oblong.............M. paniculata

Leaflets broadly ovate or oval, glaucous beneath.............

M. laevigata Plants pubescent

Leaves velvety-pubescent beneath, thick and coriaceous.......

M. viridiflora Leaves appressed-pubescent or villous beneath and scarcely coriaceous...............................M. di11enii

Loment sessile in the calyx or nearly so

Loment joints four to seven, flowers showy; leaflets not coriaceous..

M. canadensis Loment joints one to three

Leaflets scabrous, 1 to 2 inches long............M. rigida

Leaflets not scabrous, one-half to 1 inch long

Plant nearly glabrous throughout. .M. marylandica Stem pubescent; leaflets and petioles ciliate. M. obtusa