© Benaki Phytopathological Institute
Occurrence of
Viola arvensis
27
At low temperatures in the early growth
stages, juvenile stems are acaulescent, bear-
ing a rosette of leaves at the ground level
(rosette form), which may complicate identi-
fication (Figure 2). With rising temperatures,
the central stem is expanded, becoming
erect, ramose, and angular (Figure 3). The
flowers are bilaterally symmetrical, chas-
mogamous, and complete (Figure 4). They
consist of a calyx, auricled at the base, with
five lanceolate, acute sepals, and a corolla of
five petals, which are shorter than or equal
in length to the sepals. The lower petal is
white, with a small, conspicuous yellow spot
at the throat. The upper petals are creamy
white, occasionally tinged with some pink
or mauve. Flowers arise in leaf axils and are
borne singly on slender pedicels. Fruits are
3-valved capsules, which dehisce upon dry-
ing at maturity to expel the seed (Figure 5).
Mean values of basic morphological traits
are shown in Table 1.
Natural infestations of the weed were
observed in an open area of arable land
(annually disturbed environment or land in
temporary fallow) in densities ranging from
5 to 20 plants per m
2
mostly in irregular
patches. The weed populations were found
mainly in the margins (edges) of the winter
wheat field and at localities of the field with
low wheat density, in minor spring-sown le-
gumes crops such as lentils, faba beans, lu-
pine, and winged vetchling (a type of tradi-
tional Greek fava), and in parts of the field
without crop. In all these localities of the de-
fined area, there was no strong competition
for light. The occurrence of the species in
the area is probably associated with the ab-
sence of chemical control (no use of herbi-
cides) coupled with the increased nitrogen
availability in soil, which favors the overall
productivity of plants, including seed pro-
Figure 4.
Plant of
Viola arvensis
at the flowering stage.
Figure 5.
Fruit (capsule) of
Viola arvensis
.
Table 1.
Mean values of basic morphological traits of
Viola arvensis
(n = 30).
Trait
Mean
Min
Max
Plant height (maturity) (cm)
28.2
25.4
32.6
Thickness of main stem (mm)
2.6
2.2
3.0
Length of basal leaves (mm)
18.2
13.9
22.2
Width of basal leaves (mm)
14.0
10.6
16.0
Length of upper leaves (mm)
32.2
25.8
42.2
Width of upper leaves (mm)
7.8
5.6
10.2
Length of open flower (mm)
18.8
15.4
20.6
Width of open flower (mm)
15.2
12.2
17.6
Capsule diameter (mm)
5.1
4.9
5.2
Seeds per capsule
44.8
32
58
1...,19,20,21,22,23,24,25,26,27,28 30,31,32,33,34