The most prominent native conifers in Michigan are pines, and all our native species plus many from elsewhere in the world are also cultivated. In addition to those noted below, Pinus mugo and P. virginiana are noted as escapes in Ontario, and P. virginiana also in northern Indiana. See Catling (2005) for keys to native and commonly cultivated 2-needled pines in our region. The spread of non-native species of Pinus beyond cultivation has been a relatively recent phenomenon, with almost all records being in the last couple decades.
1. Needles usually 5 in a cluster, ± triangular in cross-section; membranous sheath surrounding base of each cluster deciduous; female cones cylindrical, at least twice as long as wide.
1. Needles usually 2 or 3 in a cluster, ± semi-circular in cross-section; membranous sheath surrounding base of each needle cluster ± persistent; female cones short-ovoid, much less than twice as long as wide.
2. Needles ca. (6–) 8–25 cm long, ± straight, not strongly spreading.
3. Needles mostly 3 in a cluster, the longest (6–) 8–25 cm long.
4. Longest needles 15–25 cm long.
4. Longest needles (6–) 8–15 cm long.
3. Needles mostly 2 in a cluster, the longest 8–15 cm long.
5. Needles stiff and brittle, snapping when sharply bent; buds ± reddish brown; bark of upper trunk reddish.
5. Needles flexible, not snapping when sharply bent; buds whitish, resinous; bark of upper trunk gray to dark brown.
2. Needles ca. 2–7.5 cm long, usually twisted or spreading apart.
6. Twigs brown; female cones bent apically, upper bark of trees brown.
6. Twigs pale greenish yellow; female cones ± straight; upper bark of trunk orange.