Adenanthos Obovatus - Distribution and Habitat

Distribution and Habitat

Abundant and widespread, A. obovatus occurs on a wide range of soils, favouring soils in the acidic pH range 3.9–5.4. Like most Adenanthos species it is common on deeply leached siliceous sandplain sand. It also occurs on gravelly quartz sand derived from rock outcrops, such as on the rocky hillslopes of the Stirling Range. It is rarely found on gravelly lateritic soils. It is also one of the few Adenanthos species to grow well in moist environments; it will not tolerate seasonal waterlogging—that niche is filled by A. detmoldii—but thrives in damp soils not subject to waterlogging.

Consistent with these edaphic preferences, A. obovatus is widespread and common in the scrub and heath commonly found on the sandplains of Southwest Australia, and is also common in the sedgelands that develop in moister areas of the region. It is uncommon in forest or woodland areas, because these are usually associated with lateritic soils; but it may be found in stands of jarrah or marri forest where these grow in laterite-free sand. The climate in its range is mediterranean, with annual rainfall from 625–1250 mm (25–49 in).

The species occurs in coastal regions of Southwest Australia, from Gingin and Muchea north of Perth south to Augusta and east along the south coast to Green Range, east of Albany. It also occurs in the Stirling Range, a possible disjunction; and at Narrogin, a certain and substantial disjunction. Nelson tentatively explains these disjunct populations in terms of natural climate fluctuations: during times of higher rainfall, the distribution of A. obovatus would have been much more extensive. Reductions in rainfall would cause the distribution to contract, but isolated populations could survive in favourable refugia.