External and Internal Anatomy of Plant Stems and Roots

Vocabulary flashcards covering external and internal plant stem and root anatomy, evolutionary context, cell types, tissues, shoot modifications, stem growth, and root adaptations.

First Land Plants

Algae-like organisms that appeared approximately $420$ million years ago, lacking true roots, stems, or leaves.

Plant Root Functions

Specialized plant organs that evolved for the absorption of water and minerals, anchoring, and producing hormones such as cytokinin and gibberellin.

Plant Stem Functions

Specialized plant organs that evolved for support and transport.

Plant Leaf Function

Specialized plant organ that evolved for photosynthesis.

Palms

Organisms considered giant herbs rather than true trees because their strength comes from hardened primary tissues, not secondary growth.

Basal Angiosperms

An evolutionary group of flowering plants that includes Waterlilies, Magnolias, and Laurels.

Monocots

An evolutionary group of flowering plants including Grasses, Lilies, Cattails, Palms, and Bromeliads, characterized by stem vascular bundles distributed throughout the ground tissue.

Eudicots

An evolutionary group of flowering plants including Roses, Asters, and Maples, characterized by stem vascular bundles arranged in a distinct single ring.

Primary Plant Body

The plant body derived from shoot and root apical meristems, composed of primary tissues, constituting herbaceous plant parts.

Secondary Plant Body

The plant body derived from meristems other than apical meristems, composed of secondary tissues (wood and bark), constituting woody, bark-covered parts.

Parenchyma

The most common plant cell type making up soft tissues, containing a primary wall only.

Collenchyma

Plant cell type with unevenly thickened primary walls that provides plastic (flexible) support to elongating parts.

Sclerenchyma

Plant cell type with a primary plus a thick, lignified secondary wall that provides elastic, rigid support to mature organs.

Node

The exact point where leaves, buds, or branches attach to the stem.

Internode

The region between two nodes on a plant stem.

Leaf Axil

The upper angle between a leaf petiole and the stem.

Terminal Bud

A bud that grows at the upper tip of a stem.

Bud Scales

Modified leaves that protect the delicate inner part of the bud.

Leaf Scar

A mark left on a stem where a leaf was previously attached.

Alternate Phyllotaxy

Leaf arrangement pattern consisting of $1$ leaf per node.

Opposite Phyllotaxy

Leaf arrangement pattern consisting of $2$ leaves per node.

Whorled Phyllotaxy

Leaf arrangement pattern consisting of $3$ or more leaves per node.

Distichous Phyllotaxy

Leaf arrangement pattern where leaves are arranged in $2$ rows only.

Decussate Phyllotaxy

Leaf arrangement pattern where leaves are arranged in $4$ rows.

Spiral Phyllotaxy

Leaf arrangement pattern where leaves are not aligned with their nearest neighbor.

Stolons / Runners

Specialized shoots with long, thin internodes whose leaves do not expand.

Tendrils

Modified leaves or lateral branches capable of twining around small objects.

Bulbs

Short shoots with thick, fleshy leaves, such as onion and garlic.

Corms

Vertical, thick stems covered in thin papery leaves, such as taro and crocus.

Rhizomes

Fleshy horizontal subterranean stems that allow plants to spread, such as ginger and bamboo.

Tubers

Short-lived horizontal underground storage stems with 'eyes', such as potato.

Cutin

A fatty substance encrusting outer walls, making them impermeable to water.

Epicuticular Wax

An epidermal surface layer that provides defense by making surfaces indigestible to insects and preventing fungal spore adhesion.

Stomata

Epidermal structures regulated by guard cells which contain special radial arrangements of cellulose microfibrils.

Trichomes

Epidermal projections whose functions include shading inner tissues and preventing animals from landing or chewing.

Tracheids

Water conduction passages found in all vascular plants that contain pits only (high friction) and are dead at maturity.

Vessel Elements

Water conduction passages found primarily in angiosperms that feature perforations and pits (low friction) and are dead at maturity.

Sieve Cells

Nutrient-conducting cells found in non-angiosperms, associated with albuminous cells, with sieve areas distributed all over their surface.

Sieve Tube Members

Nutrient-conducting cells found in angiosperms, associated with companion cells, featuring large sieve areas with wide pores on end plates.

Secondary Wall Thickenings in Tracheary Elements

The five structural wall thickening types present in tracheary elements: annular, helical, scalariform, reticulate, and pitted.

Protoderm

Primary tissue derivative from the apical meristem that gives rise to the epidermis.

Provascular Tissue

Primary tissue derivative from the apical meristem that gives rise to primary vascular tissues.

Ground Meristem

Primary tissue derivative from the apical meristem that gives rise to ground tissues.

Protoxylem

Xylem tissue that differentiates early, featuring annular or helical secondary wall thickenings only.

Metaxylem

Xylem tissue that differentiates late after elongation stops and possesses larger element diameters.

Protophloem

Early phloem tissue that has a functional life of approximately $1$ day before being stretched and destroyed by stem elongation.

Root Cap

Root tip structure that protects the apical meristem, secretes mucigel for lubrication, and senses gravity through starch-filled statoliths.

Quiescent Center (QC)

A central region within the root apical meristem with near-zero mitotic activity that serves as a reservoir for cell regeneration.

Zone of Maturation

Root region characterized by unicellular root hairs (∳ 10\,̢m) that double or triple the absorptive surface area.

Endodermis

Inner root layer containing Casparian strips that force selective symplastic transport of minerals into the vascular core.

Velamen

A layer of multiseriate dead cells acting as a waterproof barrier on epiphytic orchid roots.

Buttress Root

Plate-like asymmetrical root structures that stabilize tall trees by growing faster on the upper side.

Contractile Roots

Roots that shorten and pull subterranean bulbs or corms deeper into the soil.

Haustorial Roots of Parasitic Flowering Plants

Roots of parasitic plants that penetrate host stems to tap into xylem tissue.

Mycorrhizae / Mycorrhiza

Symbiotic associations between plant roots and fungi.

Ectomycorrhizae

A type of mycorrhizal association where fungal hyphae penetrate between cortical cells.

Endomycorrhizae

A type of mycorrhizal association where fungal hyphae penetrate inside cortical cells.

Root Nodules

Specialized root outgrowths formed in response to nitrogen-fixing bacteria.