Axial (stem, wood) anatomy. Cork cambium present, or absent (?); initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles (in older stems), or comprising a ring of bundles (the bundles collateral, the stems usually with a conspicuous ring of pericyclic sclerenchyma, cf. Geraniaceae); collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening absent, or developing from a conventional cambial ring.