The Geography of Phytochemical Races

98 2 Examples Within Continents
and 26°30′N, and the area within that latitudinal range where the heads are large and
many spined. Some individuals within this range are diploid; some are tetraploid.
Seaman and Mabry (1979a, b) identifi ed fi ve sesquiterpene lactones, the germacranolides
costunolide [202, R = H] and tulipinolide [202, R = acetoxy], and the
eudesmanolides costic acid [203], ilicic acid [204], and isoalantolactone [205]. The
distribution of these compounds, along with chromosome number, head size, and
range, is summarized in Table 2.20. Although there is no correlation between sesquiterpene
lactone chemistry, head morphology or location of the specimens within
the sampled range, there are some interesting connections between chromosome
number and sesquiterpenes. Tulipinolide, the acetylated derivative of costunolide,
appears restricted to tetraploids (4 of 5). This can be rationalized in terms of two
processes, one that establishes the hydroxyl function at the particular position, and
one that involves acetylation, clear-cut differences between the two ploidy levels.
Costunolide itself occurs in all fi ve tetraploids, in two of the four diploids counted,
and in several additional individuals whose chromosome numbers were not determined.
The tetraploids, all fi ve in this instance, lacked isoalantolactone and costic
acid, compounds consistently present in diploids. The only compound present in all
individuals was ilicic acid. A specimen of A. camphorata collected from a disjunct
Table 2.20 Sesquiterpenes, chromosome numbers, and fl ower head features for Ambrosia
camphorata (after Seaman and Mabry, 1979a)
Sampleb Sitec nd Heade Sesquiterpenea ISOL COSA ILLA COST TULP
17 a N 18 small 50 10 30 10 –
217 b N 18 small 10 21 57 12 –
14A c N nd small 22 – 45 33 –
15G d N nd small – 15 60 25 –
1770 e N nd small – 60 10 30 –
1804 f N nd small – 60 10 30 –
66 g N nd small – 26 74 – –
175 h S 18 large 72 16 12 – –
174 i S 18 large 51 31 18 – –
173 j S 36 large – – 38 14 48
106 k S 36 large – – 5 50 45
107 l S 36 large – – 5 50 45
171 m S 36 large – – 39 7 54
165 n S 36 small – – 56 44 –
118 o S nd small – – 14 – 86
a ISOL = isoalantolactone; COSA = costic acid; ILLA = ilicic acid; COST = costunolide;
TULP = tulipinoside; Values are relative percentage of each compound based on total
sesquiterpenes.
b Collection numbers from source paper. Small Arabic letters refer to sites on map in
Fig. 2.61.
c N = Northern group, ca. 29°–30°30′N; S = Southern group, ca. 23°30′–26°30′N.
d Meiotic chromosome number.
e Small heads with few spines; Large heads with many spines.