Morphological characters, sampling and DNA extraction
A. m. marina is widely distributed from eastern Africa, through
the Middle East, South Asia, Southeast Asia and north to South China. It
is also found in western Australia. A. m. eucalyptifolia is
mainly distributed in northern Australia and extends to southern
Philippines, western Indonesia and the Southwestern Pacific islands.
There is a significant range overlap of the two groups in western
Australia. The third putative subspecies A. m. australasica is
restricted to south-eastern Australia and northern New Zealand (Figure
1). A. m. australasica can be morphologically distinguished from
the other two groups by its fully pubescent calyx lobes and bracts
(Duke, 2006). These structures are more glabrous in the other groups.
The bark of A. m. australasica is grey fissured, with short
longitudinal fissures or reticulate lines, while barks of the other two
subspecies are smooth green or chalky white with flaky patches. A.
m. eucalyptifolia is mainly distinguished by its lanceolate leaves (as
opposed to ovate to elliptic), as well as the style in open flowers
which are positioned level with upper edges of anthers (instead of the
lower edges of anthers) (Duke, 2006). A. m. marina may also be
distinguished by its larger flowers and thicker leaves. However, these
distinctions in morphological characters may be inconclusive where two
putative subspecies coexist (Duke, 2006).
We sampled 16 populations, 577 individuals (16 to 40 individuals per
population) from East Africa, South China, Southeast Asia, Australia to
New Zealand, covering A. marina ’s range (Table 1, Figure 1).
Leaves of each individual were dried, labeled, and stored for DNA
extraction. DNA content of each extraction was measured by NanoDrop
2000. We pooled equal amounts of DNA of individuals from the same
population to make one DNA mixture. In total, 16 DNA mixtures were used
in the following experiments.