Sulfated flavonoids showed a systematic pattern among Halophila populations of the Pacific and Australia. Large-leaved plants, typical of H. ovalis (R.Br.) Hook. f., in the Palau Islands (Belau) and in Australia contained sulfated flavonoids, but small-leaved plants that have received various treatments under H. ovalis, including ssp. bullosa (Setchell) den Hartog and ssp. hawaiiana (Doty & Stone) den Hartog, and under H. minor (Zoll.) den Hartog or H. ovata Gaud. in American Samoa, Western Samoa, Tonga, Fiji, Wallis I., New Caledonia, Yap, Guam, Hawaii and Australia lacked sulfated flavonoids. Plants collected in their natural habitats as well as those grown in experimental cultures showed the characteristic patterns of these secondary compounds. Although the large-leaved plants have the potential for producing the largest leaves in the complex, they are not separable from small-leaved plants in leaf dimensions or in number of pairs of cross veins under all environmental conditions. The production of sulfated flavonoids and the potential for greater leaf length are the characteristics that can be used to separate typical H. ovalis and ssp. australis (Doty & Stone) den Hartog from other members of the complex.
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