The genus Epichloe sensu stricto includes several mating populations (biolo
gical species) of endophytic fungal symbionts of cool season grasses. To da
te, six Eurasian and one North American morphospecies have been described,
and these approximately correspond to six distinct mating populations. Here
we describe three additional Epichloe species found in natural symbioses w
ith grasses native to North America. In mating tests the three species were
not interfertile with each other or any previously described Epichloe spec
ies. Sequences of beta-tubulin gene introns, which have been useful for Epi
chloe; phylogenetics, clearly distinguished the three species, isolates of
each constituting a well supported clade. The three new species were host s
pecific: E. brachyelytri was naturally associated only with Brachyelytrum e
rectum, E. elymi only with Elymus species, and E. glyceriae only with Glyce
ria striata. While most morphological characteristics of E. elymi and E. gl
yceriae were typical of the genus, the ascus structure of E. brachyelytri w
as unique among described Epichloe species. Vertical transmission by system
ic infection of host seeds was common for E. brachyelytri and E. elymi but
never occurred for E. glyceriae. Conversely E. glyceriae developed stromata
on every infected host inflorescence (preventing its maturation), E. elymi
produced stromata on some but not all inflorescences, and E. brachyelytri
very rarely produced stromata. Thus, symbioses of the three new Epichloe sp
ecies with host grasses span the continuum from antagonistic to commensal o
r mutualistic.