Adaptive Radiation of the Hawaiian Silversword Alliance

Leaf Morphology and Anatomy

Last Modification: February 14, 2004

Leaf profiles of Hawaiian Madiinae. (A) Dubautia raillardioides; (B) D. pauciflorula; (C) D. laevigata; (D) D. microcephala; (E) D. plantaginea subsp. plantaginea; (F) D. knudsenii subsp. knudsenii; (G) D. latifolia; (H) D. imbricata subsp. imbricata; (I) D. laxa subsp. laxa; (J) D. paleata; (K) D. waialealae; (L) D. waianapanapaensis; (M) D. platyphylla; (N) D. sherffiana; (O) D. reticulata; (P) D. herbstobatae; (Q) D. arborea; (R) D. linearis subsp. linearis; (S) D. menziesii; (T) D. Scabra subsp. scabra; (U) D. ciliolata subsp. ciliolata; (V) Wilkesia hobdyi; (W) W. gymnoxiphium; (X) Argyroxiphium caliginis; (Y) A. kauense; (Z) A. virescens; (AA) A. grayanum; (BB) A. sandwicense subsp. sandwicense. A-K, T have n=14 chromosomes and are usually found in comparatively wet and shady habitats while L-S, U have n=13 chromosomes and are often found in comparatively open, dry habitats. V-BB are found mostly in open, dry habitats or bogs.
Extremes of leaf venation in the Hawaiian silversword alliance. On the left is Dubautia latifolia with pronounced reticulate venation typical of dicots. On the right is Wilkesia gymnoxiphium with parallel venation and few cross-connections. This type of venation is more typical of monocots, especially grasses. To find such extreme differences in leaf venation among very closely related species is exceptional.
Above: section of the leaf of Dubautia knudsenii, a species from a mesic forest habitat. Note the comparatively thin lamina with loosely pack cells and large air spaces in the mesophyll, and the thin cuticle on the upper and lower epidermis. Below: section of the leaf of Dubautia menziesii, a species from an arid, open habitat. Note the comparatively thick lamina with more tightly packed cells and smaller air spaces in the mesophyll, and somewhat thicker cuticle on the upper and lower epidermis.
Section of the leaf of Argyroxiphium grayanum, a species found primarily in and around the fringes of bogs. Note the compact tissue and large channels that in the intact leaf are filled with water-binding pectic compounds.
Section of the leaf of Argyroxiphium kauense, a species found primarily in and around the fringes of bogs. This leaf is very succulent, consisting of compact tissue interrupted by large channels filled with pectic compounds. The leaves of the Haleakala silversword (A. sandwicense subsp. macrocephalum), found in arid, cinder habitats are even more succulent and have a similar construction with large pectin-filled channels. These pectic materials appear to be important in maintaining a favorable water economy in arid habitats and also in bog situations where acid conditions and poor root development contribute to physiological drought. Additional Reading.

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