5.1 Formulation and definition of the characters.
The Senecio species which form the basis of this study are closely related, and there are few qualitative differences between them. The viscid indumentum which is
characteristic of S.. viscosus may be considered,
for reasons which are discussed later, a quantitative
character. Capitulum morphology in the sect. SENECIO is
generally uniform, and formal taxonomic treatments of the European members of this group (Alexander, 1975; Chater &
Walters, 1976) are largely based on quantiative
differences in capitulum size and shape, and ray floret ï
i development; ond on vegetative characters such as growth
habit and leaf shape.
The character set used in this study comprises 64
characters, of which 63 are meristic or continuous
variables and one is a multistate character. Two of the continuous characters are ratios.
Of the 64 characters, 34 are vegetative characters, 8 of these decribing growth habit, and 26 describing middle cauline leaf shape. Of the 30 capitular characters, 19 are based on the dimensions of the capitulum and its component parts, the involucre and the disc florets; 4 are indumentum characters; and 7 are ray floret characters.
The 26-character subset used to describe middle
cauline leaf shape is based on the architectural character set developed by Blackburn (1978) to classify leaves of
il A
29
Saurauia (Actinidiaceae). The definition of the vein
orders used was that of Hill (1980) whereby secondary and intersecondary veins are distinguished on the basis of rank ordering of the vein length multiplied by the vein width at the point of insertion into the primary vein. Some modification of these systems was necessary for use
with the highly dissected leaves cf Senecio. In
particular, it was necessary to define the point of origin of the apical lobe, the extent of the auricle, and the geometry of the lobes.
In the 30-character subset used tc describe the capitulum, the 4 indumentum characters were based on the relative density of two classes of trichom.es on two parts of the invulucre, the calyculus bracts and the phyllaries. Crisp (1972) characterized the leaf trichom.es cf the
British Senecic species as either glandular or
non-glandular, the non-glandular trichom.es being
subdivided into two types, 'club' trichomes with a bulbous terminal cell, and 'whip' trichom.es with a slender,
sinuous terminal cell. In this study the density of the
glandular trichomes (glands) and the non-glandular
trichomes (hairs) were treated as separate characters. Distinction was not made between the two types of hairs, because of the excessive ammount of time this would have required. Similarly, distinction was not made between the large viscid glands of S. viscosus and the smaller appressed glands of S. vulgaris, S. sylvaticus and S. squalidus. It was found that in hybrids of S. viscosus and S. squalidus the glands were intermediate in size as
well as number between these of S. viscosus and S. squalidus.
The presence of ray florets is the diasgnostic
character in distinguishing S. vulgaris var. vulgaris
(rayless) from S_, vulgaris var. hibernicus and S_. vulgaris
var. denticulatus (both rayed). As this character is
controlled by a single gene with incomplete dominance the formulation of this character was considered in seme detail.
If the genotype TnTn, the non-radiate condition in S. vulgaris, is characterized as the absence of ray florets, i.e., as a binary character (+/-) or as the meristic character 'Number of ray florets' equals 0, then the other characters based on the ray florets, e.g., length, width,
etc., are conditionally present oharacters. This has the
effect cf giving excessive weighting to the single gene which controls this polymorphism.
Two lines of evidence, however, suggest that the Tn allele controls the presence of disc florets rather than the absence of ray florets. Ingram & Taylor (1982) found that in S. squalidus in which the non-radiate condition is
also controlled by a single gene with incomplete
dominance, there was an inverse correlation between ray floret length, the development of the androecium, and the
degree of fusion of the corolla. That is, the
heterozygotes were intermediate between the ray and the disc florets in morphology as well as length.
If the Tn allele results in the alteration of the ray florets into disc florets, rather than the simple absence
31
of ray florets, then one would expect that the number of
of disc florets in non-radiate S. vulgaris would be the
same as the number of disc florets plus the number of ray
florets in S_. vulgaris var. hibernicus.
A t-test was used tc compare the number of disc florets in 15 replicates of non-radiate S,. vulgaris (Line No. 11) with 15 radiate S. vulgaris plants (Line
No. 21). Both cf these lines originally came from the
same population (Appendix 1). The non-radiate plants had a mean of 53.000 disc florets per capitulum, and the radiate plants had a mean of 44.067 disc florets per capitulum, which gave t = 3.87, p = 0.001. If the total number of florets per capitula were compared then t =
-0.06, which gives p = 0.956. That is there was no
statistically significant difference between the total
number of florets in radiate and non-radiate S.
vulgaris. For this reason the ray florets were
considered to be 'outer florets', and measurement of the characters in the non-radiate plants was done on the cuter ring of disc florets.
5.2 Materials and methods.
23 purebred lines of the 8 species and varieties; S.
vulgari s var. vulgaris, S_. vulgar is var. hibernicus, S. vulgaris var. denticulatus, S. squalidus, S. cambrensis, S. viscosus, S. sylvaticus, and S. vernalis; comprising a total of 456 plants, plus 15 interspecific hybrid lines, and one colchicine-induced autotetraploid S. squalidus
line, comprising a total of 115 plants, were grown under standardized conditions.
The 571 plants were grown in 3 batches, the first being sown on the 18th. June 1982, the second on the 9th. May 1983, and the third on the 1st. September 1983. All seeds were sown in trays of Levington ocmpost, and pricked
out at 21 days after sowing. The plants in the first
batch were potted on into 5-inch pots of John Innes No. 2 compost. The plants in the second and third batches were
grown in 5-inch pots cf soil mixture. The plants grown
in September 1983 were given supplementary lighting to
maintain a 16 hour photoperiod.
All plants were harvested on the first day of full
anthesis of the apical capitulum. Measurement of the
vegetative characters C02 to C08 (Plant Height,
Inflorescence Length, Number of Internodes, Basal Stem Diameter, Number of Leaves, Proportion of Lateral Shoots with Capitula, and Longest Leaf Length) were made on fresh material. Measurement of the length characters C02, C03,
C05 and CO8 was to the nearest millimetre. The leaf
nearest to the midpoint of the plant height (the midleaf) was removed, placed in a polythene bag, and deep frozen.
The apical capitulum was dissected, characters C35 to C47 plus character C53 were measured or counted during dissection. The calyculus bracts, the outer florets, and a sample of 10 disc florets from the center of the
capitulum, were placed on Sellctape and mounted on
microscope slides. Characters C48 to C52 and C54 to C63
33
an eyepiece graticule. Characters which were single
measurements were made tc the nearest 0.05 mm. Characters which were means cr ranges of multiple measurents were calculated to the nearest 0.01 mm.
After harvesting was complete, characters C09 to C34
were measured on the frozen leaf material. Linear
measurements were to the nearest mm, and angular
measurements were to the nearest degree. 5.3 The character set.
COl Days to Flowering.
Defined as the number of days between the seed sowing and full anthesis of the apical capitulum. C02 Plant Height.
The length from the base of the stem, defined as the cotyledon node, to the level of the stigmas of the apical capitulum.
CO3 Inflorescence Length.
The length from the apical stem node, defined as the node subtending the apical capitulum, tc the level of the stigmas of the apical capitulum.
C04 Number of Internodes.
The number of interncdes between the cotyledon node and the apical stem node.
C05 Basal Stem Diameter.
The diameter of the stem at the cotyledon node. C06 Number of Leaves.
Defined as the total number of leaves excluding the cotyledons.
G H
K
FIGURE 5.3.1 Drawing of the midleaf (MLF) of S.
vulgaris showing (a) the length characters C09 to C18, and C28, C29, (b) the angular characters C30 to C34, and (c) the Mid-Lobe characters Cl9 to C27.
35
C07 Proportion of Laterals with Capitula.
The number of lateral buds and/or branches with capitula divided by the total number of lateral buds and/or branches.
CO8 Longest Leaf Length.
Length of the longest leaf, measured parallel tc the primary vein.
C09 Midleaf Length
Maximum length cf the midleaf (MLF), defined as the leaf attached to the stem nearest tc the the midpoint of the plant height (C02). Measured parallel to the
primary vein, from the base of the auricle to the
apex of the primary vein. Length AB in Figure 5.3.1a. CIO MLF Max Width R.
The maximum width cf the midleaf, measured
perpendicular tc the primary vein on the right-hand side of the primary vein. Length CD in Figure 5.3.1a. Cl1 Mlf Max Width L.
Defined as character CIO, except measured on the
left-hand side of the primary vein. Length EF in Figure 5.3.1a.
Cl2 MLF Base to Max Width R.
Defined as the length from the base of the midleaf to the point at which CIO (MLF Max Width P) intersects with the primary vein. Length BD in Figure 5.3.1a. Cl 3 MLF Base to Max Width L.
Defined as the length from the base cf the midleaf to the point at which Cl 1 (MLF Max width L) intersects with the primary vein. Length EF in Figure 5.3.1a.
C14 MLF Auricle Length,
The maximum length cf the midleaf auricle, measured parallel to the primary vein, the auricle being
defined as that part of the basal lamina in which the 5
veins originate in the stem, i.e., below the base of the primary vein. Length BI in figure 5.3.1a.
C15 MLF Auricle Width.
Maximum width cf the midleaf auricle, measured
perpendicular tc the primary vein. Length GH in Figure 5.3.1a.
Cl6 MLF Kumber of Lcbes.
Defined as the number of secondary veins plus the
apical lobe. The apical lobe is defined as
originating at the point at which the secondary veins are cf equal thickness tc the primary vein. Point M in Figure 5.3.1b.
C17 MLF Apical Lobe Length.
Length cf the apical lobe measured parallel to the primary vein. Length KJ in Figure 5.3.1a.
C18 MLF Apical Lobe Width.
The sum of the maximum widths of the apical lobe cn
both sides of the primary vein. Measured
perpendicular to the primary vein. Length LM in /
Figure 5.3.1a.
Cl9 MLF Longest Lobe Length.
Defined as the length cf the longest secondary vein. Length OP in Figure 5.3.1a.
C20 MLF Mid-Lobe Length.
37
nearest tc the midpoint of the primary vein length. Length AB in Figure 5.3.1c.
C21 MLF Mid-lobe Max Width A.
Defined as the maximum width cf the Mid-lcbe cn the
apical side of the secondary vein, measured
perpendicular to the secondary vein. Length CD in à
Figure 5.3.1c.
C2 2 MLF Mid-Lobe FV to Max Width A.
Defined as the length from the primary vein tc the point at which character C21 (MLF Mid-Lcbe Max Width A) intersects the secondary vein. Measured parallel to the secondary vein. Length AD in Figure 5.3.1c. C23 MLF Mid-lobe Max Width B.
The maximum width cf the Mid-Lcbe cn the basal side of the secondary vein, measured perpendicular to the secondary vein. Length EF in Figure 5.3.1c.
C24 MLF Mid-Lobe PV to Max Width B.
The length from the primary vein to the point at
which character C23 intersects with the secondary t
vein. Measured parallel to the secondary vein. Length AE in Figure 5.3.1c.
C25 MLF Mid-Lobe Apical Width.
Defined as the sum of the lengths from the marginal ends of the tertiary veins adjacent tc the apex cf
the Mid-Lobe secondary vein to the points of
intersection with the secondary vein. Length GH in ^
Figure 5.3.1c.
C26 MLF Mid-Lobe Basal Width.
C27 MLF Mid-Lobe Lamina Width.
The width cf the primary lamina, from the centre of the primary vein tc the point of intersection of C26 (MLF Mid-Lobe basal Width) with the leaf margin. Measured perpendicular tc the primary vein. Length K1 in Figure 5.3.1c.
C28 MLF Intercostal Length A.
Length from the point of intersection of the Mid-Lcbe secondary vein with the primary vein tc the point of insertion of the apically adjacent secondary vein in the primary vein. Length DP in Figure 5.3.1a.
C29 MLF Intercostal Length E.
Defined as C28, except measured to the basally adjacent secondary vein. Length DN in Figure 5.3.1a. C30 MLF Apical Angle A.
Defined as the angle between the apex of the primary vein and the apices cf adjacent marginal tooth sinuses. Angle BAG in Figure 5.3.1b.
C31 MLF Apical Angle B.
Defined as the angle between the apex of the primary vein and the apices of the adjacent secondary veins. Angle DAE in Figure 5.3.1b.
C32 MLF Basal Angle A.
The angle between the base of the primary vein and the most basal auricle lobes on either side of the primary vein. Angle GFH in Figure 5.3.1b.