The Geography of Phytochemical Races

176 4 Intercontinental Disjunctions
4.1.3 Cakile (Brassicaceae)
The next example features glucosinolates in Cakile, the beach rocket. According
to Mabberley (1997, p. 113), Cakile consists of seven species that occur along the
strands of Atlantic and Mediterranean Europe, Arabia, Australia, and North America.
Rodman (1974, 1976) has the number of species somewhat higher (14), but the
subject of this section is the distribution of the genus, rather than a commentary
on taxonomy. Of special interest is the use to which Rodman (1976) has put the
glucosinolates (mustard oil glucosides) in sorting out origins and possible directions
of migration of selected species. Glucosinolates are well-known constituents
of the families comprising the order Capparales: Brassicaceae (alias Cruciferae),
Capparaceae, Moringaceae, Resedaceae, Tovariaceae, and, newly added to the list,
Setchellanthaceae (Iltis, 1999; Tobe et al., 1999).
Morphological variation in Cakile maritima Scopoli, one of the European species,
is accommodated, at least in some taxonomies (see Rodman, 1974 for details),
by recognition of three subspecies: subsp. baltica (Rouy & Roucaud) P. W. Ball,
which grows on the coast of the Baltic Sea; subsp. maritima from the western and
southern coasts of Europe, and subsp. euxima (Pobedimova) Nyárády from the
Black Sea area. Their glucosinolate profi les exhibit some striking differences. Subspecies
baltica is more homogeneous (among individuals) than most other taxa
with a profi le dominated by allyl glucosinolate [303] (see Fig. 4.3 for structures
303–311), with trace amounts of the biosynthetically related compounds: 3-butenyl
[304] and 3-methylthiopropyl glucosinolates [305] (methionine pathway). sec-Butyl
glucosinolate [306] (isoleucine pathway) is also a major component, but isopropyl
glucosinolate [307] (valine pathway) was seen only in trace amounts. The two
collections of subsp. maritima exhibited signifi cant differences as can be seen in
Table 4.1. Material from western Europe is characterized by the presence of secbutyl
glucosinolate as a major component and only a trace of the methionine-derived
3-methylthiopropyl glucosinolate, whereas material from the Mediterranean coast of
Europe exhibited a much lower concentration of the sec-butyl compound and moderate
amounts of three methylthioalkyl glucosinolates (propyl, butyl, and pentyl).
Fig. 4.3 Compounds 303–311, glucosinolates from Cakile maritima