PLANT ANATOMY Lecture 15 - Stele and Bundle Types

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Jim Bidlack - BIO 5354/4354 PLANT ANATOMY Lecture 15 - Stele and Bundle Types I. Types of steles (stellar types); stele refers to the central vascular network if the shoot and the root (includes outermost phloem and everything to the inside of it) A. Protostele 1. No pith and usually no separate vascular bundles 2. First pattern (phylogenetically) that appeared in vascular plants 3. Predominant pattern found in roots of almost all plants and shoots of lower vascular plants 4. Types of protostele a) Haplostele - xylem is a circular mass b) Actinostele - xylem margin is not smooth; it "undulates" c) Plectostele - xylem not one mass; series of plates B. Siphonostele 1. Has a pith and can have separate vascular bundles (primary growth) 2. More advanced plants 3. Found in shoots of seed plants and in roots having a broad stele (monocots) 4. Types of siphonostele a) Amphiphloic - phloem found on both sides of the xylem 1) Solenostele - very few or little leaf gaps widely separated (continuous cylinder) 2) Dictyostele - leaf gaps are abundant b) Ectophloic - phloem found only to outside of the xylem 1) Eustele (dicots) - one ring of vascular bundles surround a pith 2) Atactostele (monocots) - scattered bundle arrangement II. Stellar patterns at the node (Nodal pattern) A. Different because this is where leaves and buds are attached B. Area above & behind the leaf or bud is the leaf gap C. Area showing where the leaf (bundle(s)) attaches to stem is called leaf trace D. Examples of patterns: 1. Unilacunar, 1 trace; unilacunar, 3 trace; trilacunar, 3 trace III. Bundle types A. Collateral (common) - phloem on one side (abaxial) and xylem on the other (adaxial) B. Bicollateral (not common) - phloem on both sides of the xylem C. Amphiphloic (not common at all) - xylem in the middle surrounded by phloem D. Amphixylic (rare) - phloem in the middle surrounded by xylem E. Isolated phloem strands (random in some species) - phloem here and there (no such thing as isolated xylem strands) F. All bundle types in minor veins are collateral.

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