158 – II.3. BRASSICA CROPS (BRASSICA SPP.)
Based on cotyledonary studies of various taxa in the tribe Brassiceae, Gómez-Campo
and Tortosa (1974) proposed that Brassica evolved from the Macaronesian plant taxon
Sinapidendron. This Miocene relic survived several paleo-climatic changes that destroyed
most of the Mediterranean Tertiary flora and is put forward as the archetype from which
Brassica evolved through the Diplotaxis and Erucastrum complexes. However, the use of
such morphometric data to establish evolutionary relationships withinBrassiceae has not
always provided results that agreed with those from cytological and molecular studies.
Description
Prakash and Hinata (1980) have summarised the early taxonomic difficulties when
only morphological characteristics were used to categorise the numerous and varied
forms of the commercially important Brassica species. The early proliferation of species’
names and misclassifications resulted from the wide array of plant forms that occur
among plants within the same genome, plus the mimicking of the same morphological
features in plants with a different genetic makeup. Although the application of advanced
genetic techniques and chemical investigations has clarified relationships, there is still
some disagreement among authorities as to whether a particular form should be
considered a species, or a subspecies or variety within a species.
Brassica nigra
Figure 3.2. Illustration of a Brassica nigra plant and its parts
Source: Koehler’s Medical-Plants (1887) provided by Wikipedia, the free encyclopedia.
Sinskaia (1928) identified two major geographic forms of B. nigra, a western form
grown in Europe, Africa, Asia Minor and Afghanistan and an eastern form grown in India
and as far west as Palestine and the Syrian Arab Republic. The early forms were of short
season, spreading, with semi-erect growth up to a metre tall but taller, more erect material
was selected for commercial production (Hemingway, 1995). The prevalent annual
weedy form of today varies in height from 0.6-2.4 metres, depending on the competing
vegetation and growing conditions. The plant is lightly covered with soft hairs; the lower
