1. The stoloniferous clonal herb Glechoma hederacea (Labiatae) has a decussate phyllotaxy. Each node bears two leaves which emerge from the opposite faces of a quadrangular stolon. Anatomical studies showed that the vascular tissue of the stolon is concentrated into four major bundles, and leaf traces connect each leaf of a ramet to the proximal pair of vascular bundles. These two vascular bundles also provide the vascularization for the secondary stolon developing from the axil of that leaf. 2. Transport of resources in the vascular system was analysed using acid fuchsin dye and [.sup.14]C-labelled photoassimilate. All transport of dye in the xylem was acropetal. Leaves and unrooted secondary stolons distal to, and in the same orthostichy as, a leaf injected with dye became fully infused with dye. They were thus entirely integrated for transport of xylem-based resources. Leaves and secondary stolons in the opposite orthostichy to the injected leaf did not receive dye, and were therefore entirely independent. Leaves and secondary stolons distal to, and in the adjacent orthostichies to, the injected leaf were half impregnated with dye, and were therefore partially integrated with the injected leaf. 3. The patterns of movement of labelled photoassimilate in the phloem were qualitatively similar to the movement of acid fuchsin in the xylem, but less sectorially restricted. Although there was some basipetal movement, assimilate was predominantly translocated towards the apex. Newly developing ramets were supplied with assimilates by older ramets, but with time they became virtually independent of such support. 4. Although there is widespread physiological integration between connected ramets of G. hederacea clones, distribution is influenced by vascular constraints, relative sink strength and proximity of different parts of the clone. In addition, however, the vascular anatomy and decussate phyllotaxy of the species has a very marked effect on the patterns of resource movement which occur within and between stolons. As clones grow and acquire greator structural complexity, they change from having complete integration, to become a number of semi-autonomous integrated physiological units (IPUs). Different stolon branches are in different IPUs. Such a structure may be superior to a system of integrated branches for exploring a heterogeneous habitat. 5. Defoliation experiments showed that although vascular anatomy limits translocation from sources to sinks in different orthostichies, the balance of such translocation can probably be modified, and source -- sink relationships changed, when severe conditions are imposed upon a part of a clone. Under such conditions there appears to be an increase in translocation between orthostichies. 6. The information obtained in these investigations highlights the value of using complementary anatomical and physiological methods to analyse the relationships between form and function in plants. In clonal species such as Glechoma hederacea, the rate at which different branches grow, and therefore the rate of gain and loss of ramets, depends on source -- sink relationships between ramets. Thus, unless the physiological relationships between ramets are understood, little progress can be made in understanding ramet population dynamics. Key-words: integrated physiological units, orthostichies, photoassimilate distribution patterns, ramet population dynamics, sectoriality Journal of Ecology 1992, 80, 25-38