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All members of the Hawaiian silversword alliance are perennial but they encompass a remarkable range of size and habit categories including monocarpic rosette shrubs such as Argyroxiphium sandwicense ssp. macrocephalum, |
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subherbaceous mat-forming species (Dubautia scabra), |
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cushion plants (Dubautia waialealae), |
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spreading shrubs like Dubautia raillardioides, |
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upright shrubs such as Dubautia microcephala, |
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trees like Dubautia knudsenii |
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and Dubautia reticulata, |
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and even a liana (Dubautia latifolia). |
The different growth forms illustrated here are among the most obvious evolutionary adaptations spawned by the original colonizing ancestor of the silversword alliance in the Hawaiian Islands. This ancestor may have been a creeping, mat-forming species similar to the North American tarweed, Raillardiopsis murii. The shifts in stature and habit seen here probably were critical to the success of the rapidly diverging members of this alliance when competing with other plants for light and other resources in extremely varied habitats ranging from near sea level to the upper limits of plant growth on the higher volcanic domes of the Hawaiian archipelago.