M. longifolium (Hook.) Brid., Bryol. Univ. 1: 309. 1826.
Orthotrichum longifoliumHook., Musci Exot. 1: pl. 44. 1818.
Macromitrium homahcronC. Miill., Bull. Herb. Boissier5:197.1897.
Macromitrium cirrosum has smooth setae and smooth to
slightly plicate capsules, while M . longifolium has papillose
setae and strongly 8-plicate capsules. Gametophytically it is
difficult to differentiate the two. Macromitrium longifolium
tends to have longer, more slender leaves which are undulate,
particularly when moist, and often glossy. Macromitrium cirrosum can also have these characters, but they are more pronounced in M . longifolium. Both ofthese species are large, irregularly branched, and differentiated from other Mexican species by long, slender leaves, entire basal margins, and tuberculate basal cells.
I see no distinct differences between M . homalocron and
M . longifolium. The literature suggests differences in leaf
undulation and seta length as well as calyptra hairiness, but I
find no definite correlations.