Manihot Manihotoides (Euphorbiaceae) - CNCFlora

Introduction 9
We believe, however, that by employing well-designed computer programs, analyzing
many characters for each taxon, and keeping the concepts of biosystematics in mind, we
have given a more than adequate reflection of the intraspecific and interspecific relations
in Manihot. By examination of the Table of Characters and Attributes Employed (Table
I), one may determine precisely the basis upon which our classification rests, and the
processes by which decisions were made. Although some of the species are represented by
single, inadequate specimens, by comparisons of these with those species which do have
adequate representation, and using the same objective measure for delimitation of the
taxa in all cases, a unified classification has been produced.
We have no doubt that when more information for some of the species becomes
available, there will have to be new combinations, changes in taxon level, and even
reduction of some of our taxa to synonymy. Even with the most sophisticated methods
of analysis of the data, final judgment of the taxa to be recognized must be based on the
knowledge and skill of the taxonomist, and we are certainly open to mistakes in these
areas.
Growth habit
The species of Manihot are perennial, and vary in growth pattern from nearly
acaulescent subshrubs to small trees with trunk diameter (DBH) of 25.0 cm and heights
of 10 to 12 m. Decumbent subshrubs, semiherbaceous subshrubs, shrubs, and small trees
are found in the genus. The branching pattern is typically dichotomous or trichotomous,
the point of branching determined by the appearance at the branching point of a terminal
inflorescence. Bark of the woody species is generally smooth, but in some cases (as in M.
caudata) may become slightly scaly with age. Many of the species are lacticiferous, and
two rubber-producing species, (M. glaziovii and M. caerulescens subsp caerulescens) are
still cultivated to some extent.
Many of the stems of subshrub and shrubby species, adapted to regions of marked
dry periods, die back to a root crown regularly, and other larger shrubs regularly lose
their leaves during the dry season. Adaptation to arid conditions is further indicated by
the presence of enlarged storage roots.
Pigmentation
Colors vary in Manihot species from dark brown to light tan in the roots, from
brown to gray to yellow or red in the stems, from red to yellow to green on the petioles,
and from red to green in the flowers. Since perception of color varies with the eye of the
observer, and with age of the plant part observed, and since the observations are not
consistent over a sufficiently large number of specimens, we have not been able to
employ pigmentation as systematic criteria. The senior author has employed the
Nickerson Color Fan of the American Horticultural Council in all collections made by
him, and these are consistently reported in the species descriptions. Both the official
color designation, and the associated numeric notation, which follows the Munsell color
classification, are provided (where available) in the species descriptions. For example, for
the petiole, the following notation may be found: "brilliant yellow green (5GY 8/8)."
Although this is a very precise notation, it is recognized that it is still subject to the same
limitation noted above.
Roots
Many of the species of Manihot have tuberous roots. Unfortunately, there are
insufficient samples of this organ associated with herbarium specimens (particularly in the
South American material) to employ characters from them as systematic criteria. Of
those species we have examined, there are indications that many valuable characters are