The Geography of Phytochemical Races

16 2 Examples Within Continents
Fig. 2.7 Compounds 26–30
from Duboisia myoporoides
2.2.3 Zieria (Rutaceae)
Zieria, a genus of about two dozen species in Rutaceae, is endemic to eastern
Australia, including Tasmania, except for one species, Z. chevalieri Virot, which
is a native of New Caledonia. A detailed study of the genus has shown it to be a
rich source of secondary compounds, including a cyanogenic glucoside (based on
p-hydroxybenzaldehyde) (Flynn and Southwell, 1987a) and an array of simple phenolic
and terpene-derived volatile compounds (Flynn and Southwell, 1987b). We
are interested here is an examination of chemical variation within the genus studies
carried out by Southwell and Armstrong (1987). Collections of the Z. arborescens
Sims aff. arborescens-smithii group from Tasmania and along the southern coast
of Victoria, north to the area around Cooktown, Queensland (Fig. 2.6) provided
an interesting picture of biosynthetic specialization over a range of 25° of latitude.
There is a signifi cant decline in the zierone [31] (see Fig. 2.8 for structures
31–40) content and a corresponding increase in the phenolic ethers, eugenol [32],
safrole [33], elemicin [34], 2,3,4,6-tetramethoxystyrene [35], and 2,6-dimethoxy-
3,4-methylenedioxystyrene [36], as one goes northward from Tasmania to northern
coastal Queensland. Although there is a moderate degree of variation among populations
in any given area, the overall trend in carbon utilization in the biosynthesis
of these different classes of compounds is impressive.
Other observations on chemical variation within Zieria can be mentioned at this
point. Zieria cytisoides “form b” occurs along the coast of New South Wales and in
similar habitats in Tasmania. Five populations concern us here, two from the former
area and three from the latter. Signifi cant differences in the concentration of the monoterpene
derivative (−)-chrysanthenone [37] were observed by Southwell and Armstrong
(1987). The populations on the mainland exhibited concentrations of the ketone of
15% and 18%, whereas those in Tasmania had higher amounts, that is, 42%, 49%,
and 55%. The New Caledonian Z. chevalieri was shown to exhibit an unusual profi le
of compounds, relative to the Australian species, with 2,4,6-trimethoxystyrene [38],