Announcements:
Remember, your next lab (Laboratory 2) will be held in the Conservatory and adjacent rooms of the Plant Sciences Laboratory (PSL). Meet your TA in front of Room 1201 PSL. Bring these notes, your Class Notes (it has the lab), and your textbook.
If you haven't done so already, please hand in the Student Information sheet distributed during lecture 1.
Prof. Downie is currently studying at the University of Texas, Austin. He will be returning to class on Monday, January 26th.
Four Main Components of Taxonomy
Description or Phytography
In this lecture, we will look at phytography, the science of plant description, by focusing on flowering plant vegetative morphology.
Taxonomic Characters
Taxonomic characters are fundamental to the science of taxonomy. They provide the basic information for classification, they are the features used in identification, they are used to determine relationships, and they give the basis for the naming of taxa.
Definition: Any attribute of an organism that can be consistently measured, counted, described, or otherwise assessed (ex., leaf shape, plant height, stamen number, pigment type).
It is useful to distinguish between character and character state. A character state is one of the various conditions (or values) of a character observed across a group of taxa. It is the fundamental unit of a character. A character is a group of states considered to be modifications or alternate forms of basically the same thing.
Examples of Characters and Character States:
- Character: leaf margin; Character states: entire, crenate, serrate, dentate.
- Character: flower color; Character states: red, white, blue.
- Character: life span; Character states: annual, perennial, biennial.
- Character: leaf venation; Character states: pinnate, palmate, parallel.
- Character: pigment type; Character states: anthocyanin, betalain
- Character: nucleotide at position 112 in rubisco gene; Character states: A, C, G, T.
How would you describe these plants?
Plant 1
Plant 2
Mentha arvensis L. Field mint.
Plants herbaceous, aromatic; stems quadrangular, ascending or erect, 2 – 8 dm, pubescent with few to numerous, short and retrorse to longer and more spreading hairs, often glabrous between the angles; leaves simple, opposite, short-petiolate, the blade 2 – 3 cm × 6 – 40 mm, glabrous or hairy, serrate, acuminate, with several pairs of lateral veins, rather narrowly ovate to more often somewhat rhombic-elliptic, those of the inflorescence, at least, tending to be cuneately tapered to the petiole; verticils compact, axillary to the scarcely reduced (middle and) upper leaves, and separated by internodes of fairly ordinary length; calyx pubescent, 2.5 – 3 mm; corolla white to light purple or pink, 4 – 7 mm, rarely casually 5-lobed; 2n = 24 – 96. Moist places, especially along streams and shores; circumboreal, in Amer. s. to N.C., Mo., and Calif. Native Amer. and e. Asian plants, as here described, are var. canadensis (L.) Kuntze. The European var. arvensis, with the lvs of the infl relatively broader, more ovate, and somewhat broadly rounded to the petiole, is intr. from Nf. to Que. and Pa., but extremes of one var. could pass for the other.
Gleason and Cronquist, 1991, Manual of vascular plants of northeastern United States and adjacent Canada. The New York Botanical Garden, Bronx, NY.
General objectives:
After studying this material you should be able to:
- Have a basic and working knowledge of flowering plant vegetative morphology. There is a bewildering large number of terms but in this course we will stress only some of the more commonly used ones.
- Be able to draw, compare, and contrast each of these terms.
- Know the relationship between each of the terms listed (i.e., character states) and the major category to which they belong (i.e., character).
Text and Other Resources:
Plant Systematics, A Phylogenetic Approach, Third Edition by Walter S. Judd et al.: Taxonomic Evidence: Structural and biochemical characters.
- Chapter 4, Morphology, pages 53 – 61
Digital Flowers. Once in the program, access Morphology: Vegetative.
Other web resources:
The links below lead to supplementary information offered by other on-line systematic courses at other universities or sources. Please use with caution, as some of the information presented may be different from what we cover in IB335.
Vegetative Morphology
Life Span
ANNUAL – completes life cycle in one growing season (one year)
BIENNIAL – completes life cycle in two growing seasons (two years). First year vegetative; second year flowers & fruits
PERENNIAL – lives for more than two growing seasons (more than two years); perennials may be woody or herbaceous (the latter with underground perennating structures)
Plant Habit
HERB – no above ground persistent woody tissue but may have underground perennating structures; may be annual, biennial, or perennial
SUBSHRUB (=suffrutescent) – lower stems woody but upper stems herbaceous (prefix "sub" means "almost")
SHRUB – a woody low-stature perennial plant with one to many slender trunks arising from near its base
TREE – a large woody perennial plant with one to several relatively massive trunks and an elevated crown
SUCCULENT – possessing thick, usually soft, watery leaves and/or stems. Stem succulents & leaf succulents
VINE – a woody or herbaceous plant with a long, slender, more or less flexible stem which cannot support itself
LIANA – a woody, climbing vine (characteristic of the tropics)
Roots
- usually the portion of the plant that absorbs water and minerals
- mostly underground
- principal organ of attachment
- lacks nodes and buds (a node is that portion of the stem where the leaves originate)
Stems
- leaf-bearing main axis of a plant
- aerial or subterranean
- divided into nodes and internodes
- gives rise to branches, leaves, and flowers
Leaves
- lateral appendages on a stem
- usually serves as the primary photosynthetic surface of the plant
- can be extremely modified in morphology
Root types
TAPROOT – central main root that descends vertically; larger than any branching root
FIBROUS – thin thread-like roots arising from a taproot or from stem tissue
ADVENTITIOUS – roots that originate from any part of the plant other than the root system
Question: Why is a rhizome considered an underground stem and not a horizontal root?
Stem types
AERIAL – an erect or prostrate stem (the most common type)
RHIZOME – an underground horizontal persistent stem; its leaves are often reduced to scales and it usually bears adventitious roots and buds
STOLON – a horizontal stem near the ground surface that produces new plants at its nodes or tip (runner)
BULB – a thickened, underground short vertical stem with large storage leaves; usually borne below ground
CORM – a solid, erect underground stem with leaves absent or dry and scale-like
TUBER – a solid, enlarged, underground horizontal stem that serves as a storage area for food reserves
Photos of modified stems
Stem features
Photo of a woody twig
NODE – the position on a stem where a leaf or bud is or was attached
INTERNODE – the portion of a stem between two nodes
AXIL – the upper angle between a leaf (or any other lateral structure) and the stem to which it is attached
AXILLARY BUD – a bud borne in the axil of a leaf (also called a lateral bud)
BUD – the structure giving rise to a leafy stem, a flower, or both; it may be naked or protected by bud scales or stipules; it may be lateral or terminal
BUD SCALES – scale-like leaves that protect the buds
BUD SCALE SCARS – scars remaining when the bud scales fall off
STIPULES – usually a pair of appendages located at the base of a leaf but may be fused into a ring around the stem; variable in size, shape and texture; serves for protection or to attract pollinators
Types of Stipules
STIPULE SCARS – a pair of scars or a single ring-like scar when stipules fall away
LEAF SCAR – the scar left when a leaf falls from a twig; it contains one or more vascular bundle scars
Leaf persistence
EVERGREEN – bearing green foliage all year round
DECIDUOUS – the loss of leaves during unfavorable conditions (such as at the end of each growing season)
Leaf parts
LEAF BLADE – expanded portion of a leaf
PETIOLE – stalk of a leaf
STIPULES – the pair of appendages located at the base of a petiole
HINT: The presence of an axillary bud is very important to help identify where the leaf begins. Look for it above the petiole. Everything above the axillary bud is all one leaf.
Leaf complexity
SIMPLE LEAF – a leaf with a single blade (it is not divided into leaflets; there is always a flange of blade tissue connecting adjacent lobes)
COMPOUND LEAF – a leaf with more than one blade per petiole (it is made up of two or more leaflets and these leaflets are wholly separate)
PETIOLULE – the stalk of a leaflet
LEAFLET – one of the segments of a compound leaf
RACHIS – the axis of a pinnately compound leaf
PINNATELY COMPOUND – a leaf in which there are more than three leaflets arranged in two rows along a common axis. The leaflets are attached like the vanes of a feather
PINNA (pl. PINNAE) – the primary division (or leaflet) of a pinnately compound leaf
BIPINNATELY COMPOUND – leaf divided twice
Photo of bipinnately compound leaf
TRIPINNATELY COMPOUND – leaf divided three times; a pinnule is the ultimate division of a 2- or 3-times compound leaf
Photo of tripinnately compound leaf
PALMATELY COMPOUND – where the leaflets arise from a common point of attachment; there is no rachis
TRIFOLIOLATE – a compound leaf with three leaflets
TRIFOLIATE – three separate leaves arising from the same node
Simple leaf or compound leaf?
Leaf attachment
PETIOLATE – having a petiole
SESSILE – lacking a petiole (or leaf stalk)
SUBSESSILE – a very short petiole
SHEATHING – leaf base enwraps stem
Leaf arrangement
BASAL – leaves attached to rhizome or other underground stem
CAULINE – leaves attached to above-ground stem
- ALTERNATE – one leaf per node
- OPPOSITE – two leaves per node
- WHORLED – three or more leaves per node
Leaf venation
PINNATE – consisting of a central mid-vein with many secondary veins emerging on both sides to form a feather-like pattern
PALMATE – all primary veins arise at the same point at the base of the leaf
PARALLEL – veins lie more or less parallel to the leaf margins
Leaf blade shape
LINEAR – long and narrow with the sides parallel (>4:1)
OBLONG – nearly rectangular with the sides parallel (2-4:1)
LANCEOLATE – spearshaped; widening above base and then long tapering to apex (3-4:1)
OVATE – eggshaped; broad nearest base (<3:1)
OBOVATE – ovate, but with narrower end towards point of attachment
HINT: The prefix "ob" means opposite, so "obovate" is the opposite of "ovate."
ELLIPTIC – ellipse shaped; widest near middle and tapering at both ends
ORBICULAR – circle shaped
RENIFORM – kidney shaped
Leaf apices
ACUTE – sharp, ending in a point with straight sides to the apex (<90 degrees)
ACUMINATE – sharp, ending in a long-tapering point with concave sides
OBTUSE – blunt, rounded (>90 degrees)
MUCRONATE – a small, abrupt point
Leaf bases
ACUTE – sharp, <90 degrees
ACUMINATE – sharp, long-tapering point
OBTUSE – blunt, >90 degrees
CORDATE – heart shaped (equal rounded lobes at the base)
OBLIQUE – unequal sized lobes at base
PELTATE – umbrella like; the petiole is attached to the blade inside of the margin; often orbicular in shape
Leaf margins
ENTIRE – a margin without any toothing or division (smooth)
CRENATE – scalloped or round-toothed
SERRATE – a saw-toothed margin with sharp teeth pointing towards the apex
DENTATE – sharp teeth projecting at right angles from the margin
PINNATELY LOBED – lobed towards the midrib but not reaching it
PALMATELY LOBED – lobes all arising from one point at the base of the leaf
Surface features
GLABROUS – lacking hairs (trichomes); a smooth surface
PUBESCENT – covered with hairs (also called trichomes)
STELLATE – hairs that branch at or near their base (star-shaped from above)
GLANDULAR – hairs that bear glands (that break down into sticky beads of fluid); they may be stalked (stipitate) or sessile
Special features
TENDRIL – an elongated, twining segment of a leaf, stem, or inflorescence by which a plant clings to its support
THORN – a woody, sharp-pointed, modified stem (has stem-like vasculature)
SPINE – a sharp-pointed modified leaf or leaf part
STIPULAR SPINE – borne in pairs and lateral to leaf (or leaf scar)
PRICKLE – a sharp pointed outgrowth from the epidermis
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