Lycopod specific features including appearance of microphylls, wide spectrum of phyllotaxis, high frequency of phyllotactic transformations, shoot dichotomy significantly affect their vasculature and make it exceptional in plants. Partitioning of the stele into vertically oriented protoxylary ribs (PXRs)affects the pattern of the vascular connections with microphylls. The number of PXRs in the stele is not correlated to the type of phyllotactic pattern or its expression. In shoots with whorled phyllotaxis microphylls from one to three phyllotactic ortostichies connect to one PXR. In shoots with helical phyllotaxis the vertical course of PXRs and the regular microphyll pattern cause the characteristic "zig-zag" course of stelar parastichies: each PXR supplies microphylls from different foliar parastichies - traced on the surface of the stem. As each trace connects to the nearest vertical PXR, the microphyll traces must vary in length, unlike as in seed plants where megaphyll traces are of rather equal length. The regulating role of the apex is expressed by efficient packing of primordia and its control of the stelar diameter. During dichotomy of the shoot, circumferential discontinuity of the microphyllous phyllotaxis is paralleled by the reconstruction of the stelar system: the change of a stele symmetry and architecture. Changing number of PXRs is associated with appearance of endarchic protoxylem elements inside of the stele. Parallelism of the stem and stele surfaces, with regularly distributed elements, results in spatial adjustment of microphyll and PXR patterns. In this light lycopod vasculature seems to be the first, maybe imperfect yet, supplying system for superficial elements.

Key words: dichotomy, Lycopodium, morphogenesis, phyllotaxis, stele, vascular system