In spite of the term 'endophyte' being employed for all organisms that inhabit plants,
mycologists have come to use the term 'fungal endophyte' for fungi that inhabit plants
without causing visible disease symptoms. The term refers only to fungi at the moment
of detection without regard for the future status of the interaction. This paper is
a review of literature on non-balansiaceous fungi involved in asymptomatic colonisations
of plants. These fungal endophytes represent a continuum of fungi with respect to
physiological status, infection modus, colonisation pattern, secondary metabolism,
life-history strategy, and developmental and evolutionary stages, but also with respect
to the fungal and host taxa involved in the symbioses. We hypothesize that there are
no neutral interactions, but rather that endophyte-host interactions involve a balance
of antagonisms, irrespective of the plant organ infected. There is always at least
a degree of virulence on the part of the fungus enabling infection, whereas defence
of the plant host limits development of fungal invaders and disease. It is also hypothesized
that the endophytes, in contrast to known pathogens, generally have far greater phenotypic
plasticity and thus more options than pathogens: infection, local but also extensive
colonisation, latency, virulence, pathogenity and (or) saprophytism. This phenotypic
plasticity is a motor of evolution.