Data from studies of morphology and cytogenetics 
now seem to justify the presentation of a new hypothesis 
regarding the origin of ‘Tripsacum, an hypothesis that 
has already been described in a preliminary statement 
by the senior author (Galinat, 1964). It now seems possi- 
ble that Tripsacum has a closer relationship to maize than 
has previously been suspected; Tripsacum may be an 
ancient amphidiploid hybrid between wild maize and 
another grass, probably Manisuris (Plate XLVI). 
MorpPHOLOGICAL EVIDENCE 
Even though evidence from histological characters has 
been essential in determining the probable phylogeny of 
certain grasses (Avdulov, 1931 and others), the early 
stage of our investigations permits consideration here of 
only the more traditional taxonomic characters based on 
gross morphology. In this case, however, they are sup- 
ported by evidence from cytogenetics. 
Previous taxonomical, morphological and cytological 
evidence suggests that Tripsacum is closely related to 
Manisuris and may even be a polyploid hybrid having 
Manisuris as at least one of its parents. Among the 
genera of the tribe Andropogoneae, Manisuris shows 
closest morphological relationship to the maize tribe, 
Maydeae, especially to Tripsacum (Weatherwax, 1935). 
Indeed, Manisuris has in the past been regarded by some 
taxonomists as a species of T'ripsacum (Michaux, 18083— 
cf. Hitcheock, 1935). As noted by Mangelsdorf and 
Reeves (1939): ‘‘The most striking differences between 
the two genera are that Manisuris has perfect flowers and 
Tripsacum does not and that Tripsacum has the stami- 
nate and pistillate spikelets in separate portions of the 
inflorescence ; and these differences may not be sufficient 
justification for considering the relationship of the two 
genera to be very remote.”” ‘I'wo of the nine species of 
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