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8. MOLECULAR PHYLOGENY OF THE GENUS LOLIUM
into species began about 1 MYA (Charmet et al. 1997). There is no doubt that the species
within Temulentum clade should be older than 2000 years. Darnel, L. temulentum has been
mentioned in the Bible, whose age is dated to 3500 years. When the divergence is estimated
based on t=D/2α transformation, the respective values are as follow: the divergence of
L. persicum from a common stock about 1.3 MYA, and the split of L. remotum and L. temulentum
about 0.95 MYA. These values seems realistic in comparison both with 1 MY based
on cpDNA (Charmet et al. 1997) and data from the other studies.
On the other hand, it is feasible that the Temulentum clade species observed nowadays
resulted from a kind of unintended domestication during the development of agriculture.
Domestication involves selection of seeds and modification of a number of traits
including growth habit, plant architecture and the mode of reproduction. Growing in the
field, between primitive crops, they might have been unrecognisable and harvested together
with a crop. After some time first farmers might have learnt to recognise them as
weeds and eliminate during a growth. Only individuals harvested with crops might have reproduced
next season and thus only these plants were selected that were able first, not
to be recognized, second, to produce seeds during a year. Crop mimicry i.e., the weed
looks identical to the crop or weed seeds may be impossible to separate, has been particularly
prevalent in grain cereals (Hancock 2005). Notably, self-pollination might have
been an adaptation to growing with cereals and thus could have emerged late in the evolution
of this group. The morphological similarity of L. temulentum seeds to barley or wheat
or L. remotum seeds to flax seeds are the tangible evidences for the proposed scenario.
L. persicum mimics the appearance of cereals so well that it can grow in cereal fields up it
is to late. Therefore, it has become especially troublesome weed in the USA, where it has
been introduced. As it is documented for such domesticated species as maize, barley and
the others they do not differ from their progenitors making a single biological species. It is
likely therefore, that today we are looking at domesticated forms of species belonging to the
Temulentum clade. They differentiated about 0.95-1.3 MYA as estimated in the current studies
and they were domesticated about 10 000 years ago together with the development of
primitive agriculture.