Stem Morphology and Anatomy – Key Vocabulary

These flashcards cover fundamental vocabulary related to stem structure, development, tissue systems, phyllotaxy, and vascular arrangements as discussed in the lecture.

Stem

Above-ground plant axis that supports leaves, flowers, and fruits while transporting water, nutrients, and photosynthates.

Shoot Apical Meristem (SAM)

Primary meristem at the tip of a shoot that generates all primary stem tissues and lateral organs.

Primary Stem

Stem tissues produced directly by the shoot apical meristem before any secondary thickening occurs.

Secondary Thickening / Secondary Stem

Increase in stem girth produced by the vascular cambium (secondary xylem and phloem).

Phytomere

Repeating shoot unit consisting of a node, leaf, axillary bud, and the following internode.

Node

Stem region where a leaf and its axillary bud are attached.

Internode

Stem segment between two successive nodes; principal zone of elongation.

Axillary Bud

Dormant or active shoot meristem located in the leaf axil; may develop into a branch or flower.

Phyllotaxy

Species-specific arrangement of leaves on a stem determined at the SAM.

Fibonacci Series (in plants)

Mathematical sequence (1,1,2,3,5,8…) that describes the divergence angles seen in many spiral phyllotactic patterns.

Alternate Leaves

Phyllotaxy where single leaves arise one per node, sequentially on different sides of the stem.

Opposite Leaves

Phyllotaxy with two leaves emerging at the same node on opposite sides of the stem.

Distichous

Opposite leaves arranged in two rows along the stem.

Decussate

Opposite leaves arranged in alternating right-angle pairs, forming four rows.

Collenchyma

Living ground-tissue cells with unevenly thickened primary walls, providing flexible support.

Cortex

Ground-tissue region between epidermis and vascular tissue in stems and roots.

Pith

Central ground-tissue region inside the vascular ring; often parenchymatous and storage-rich.

Dermal Tissue System

Outermost tissue layer (epidermis + cuticle) that protects the stem and regulates gas exchange.

Ground Tissue System

Bulk tissue (cortex + pith) functioning in storage, support, and metabolism.

Vascular Tissue System

Conducting tissues—xylem and phloem—organized into bundles or cylinders.

Vascular Bundle

Discrete strand of xylem, phloem, and associated fibers within a stem or leaf.

Eustele

Ring of discrete vascular bundles surrounding a pith; typical of eudicot and gymnosperm stems.

Atactostele

Scattered vascular bundles throughout ground tissue; characteristic of monocot stems.

Protostele

Solid central core of xylem with peripheral phloem; typical of most eudicot roots.

Siphonostele

Vascular cylinder with a central pith surrounded by xylem and phloem; common in monocot roots.

Xylem

Vascular tissue that conducts water and minerals upward; composed of tracheary elements and fibers.

Phloem

Vascular tissue that transports sugars, hormones, and other solutes from sources to sinks.

Protoxylem

First-formed, narrow xylem elements that mature while the organ is still elongating.

Metaxylem

Later-formed, wider xylem elements that mature after elongation ceases.

Endarch

Xylem maturation pattern in stems where protoxylem is interior and metaxylem exterior.

Exarch

Xylem maturation pattern in roots where protoxylem is exterior and metaxylem interior.

Protoxylem Lacuna

Cavity left after protoxylem elements rupture during stem elongation.

Bicollateral Phloem

Vascular bundle type with phloem on both outer and inner sides of the xylem (e.g., tomato, cucurbits).

Leaf Trace

Vascular strand that diverges from the stem bundle to supply a leaf.

Branch Trace

Vascular strand that connects the stem’s vascular system to an axillary bud, enabling branch formation.

Leaf Gap

Parenchymatous interruption in the stem’s vascular cylinder above a departing leaf trace.

Euphyll (True Leaf)

Leaf type in vascular plants characterized by a leaf gap and complex venation.

Anticlinal Division

Cell division with new wall perpendicular to the surface, increasing surface area.

Periclinal Division

Cell division with new wall parallel to the surface, adding new tissue layers.