Stern and rhizome anatomy is reported for Anemopsis californica Hook., Houttuynia cordata Thunb., and Saururus cernuus L. Secondary growth is reported for the first time in Saururaceae. Cambia function indefinitely in Anemopsis in both fascicular and interfascicular areas. Interfascicular cambium is minimal in Saururus and absent in Houttuynia; fascicular cambium is present in both genera and produces a finite quantity of vessels, fiber-tracheids, and axial parenchyma but no rays. Anemopsis has vessels with simple perforation plates plus tracheids in wood, suggestive of adaptation to fluctuating water availability. The scalariform perforation plates of Houttuynia and Saururus suggest an unbroken history of occupancy of mesic habitats. Ethereal oil cells are reported for rays of Anemopsis, and for pith and cortex of the three genera studied. Stern idioblasts and other histologieal details are ineluded along with wood data in anatomical deseriptions of sterns. DNA data as weIl as maeromorphologie al data implicate Saururaeeae, along with Aristolochiaceae, Lactoridaceae, and Piperaceae as paleoherbs elose to the origin of monoeotyledons. Key wood features that unite these families are cited. Chloranthaeeae, whieh share stern endodermis and sealariform perforation plates with Saururaeeae, are also considered elose. Features of Saururaceae that are analyzed with respeet to monoeotyledon origin inelude loss of interfaseieular cambium, minimization of faseieular cambium, lack of imperforate traeheary elements in monocotyledon bundles, trimery, the sympodial habit, and production of adventitious roots.
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Carlquist et al. (1995) studied this question.