I've been wondering for awhile, so I asked the Plant Taxonomy/Vascular Plants instructor at my university. Not being 100% sure I had all the differences I decided to look it up; add information or clarify if you can.


Leaf = Modified stem outgrowth that conducts photosynthesis or reproduction. "Leaf = The main photosynthetic organ of most green plants, consisting of a lateral outgrowth from a stem and comprising *lamina , *petiole , and leaf base. (See lamina for the different kinds of leaf shapes and leaf margins.) There are usually a great number of leaves on any one plant, although these may be lost in the colder or drier months in deciduous plants. A leaf typically consists of conducting tissues and photosynthetic cells (the *mesophyll ) often differentiated into *palisade and *spongy mesophyll , surrounded by *epidermis. The epidermis is perforated by *stomata, usually more numerous on the abaxial (lower) side of the leaf. The epidermis is usually covered by a waxy cutinized layer termed the *cuticle. This prevents excessive water loss by transpiration. In many plants, however, leaves may be reduced or even absent, as in many xerophytes. Sepals, petals, and bracts are considered to be modified leaves and many believe the stamens and carpels are also derived from leaves. See also microphyll , megaphyll."

Types of true leaves: 1. Microphylls 2. Megaphylls (size is not diagnostic).

1. Microphylls (only known to members of Lycopodiophyta) - 1 vascular trace, vascular gap absent, leaf veination absent. [arose via the enation theory].

2. Megaphylls (known to most vascular plants [Tracheophytes]) - multiple vascular traces, vascular gap present, leaf veination present. [arose via the telome theory].


"Phyllode = A more or less flattened petiole resembling and performing the functions of a leaf. Vertically expanded petioles are seen in a number of Acacia species. The leaves of many monocotyledons are believed to be of phyllode origin. Compare cladode." Phyllode: A leaf modification beneficial for photosynthesis in xeric environments.

"Cladode (phylloclade) = A specialized stem structure resembling and performing the functions of a leaf. Examples are the stem joints or pads in Opuntia (prickly pears) and the 'leaves' of Ruscus aculeatus (butcher's broom). In these genera the true leaves are reduced to spines or scales respectively. The formation of cladodes is an adaptation to arid conditions. A cladode may be distinguished from a leaf by the presence of buds on its surface. Compare phyllode."

"Petiole = The stalk that attaches the leaf lamina to the stem. The point of attachment is often strengthened by a widening of the base of the petiole. Some leaves (sessile leaves) lack a petiole and are joined to the stem at the base of the lamina. Sessile leaves are characteristic of most monocotyledons. The petiole is generally similar in structure to a stem except that the vascular and strengthening tissues are asymmetrically arranged so as to bear the weight of the lamina. The different patterns of veins evident in petioles are useful taxonomically. Various modifications of the petiole are seen. Some are flattened and bladelike (see phyllode ). Others are inflated, as in Eichhornia crassipes (water hyacinth), where they aid buoyancy. In many species the base of the petiole sheaths the stem, as in Heracleum mantegazzianum (giant hogweed). The base of the petiole may be modified as a *pulvinus. The petioles of some climbing species, e.g. Clematis, are haptotropic. The base of a fern rachis is sometimes termed a petiole."

"Lamina (blade) = 1. The usually flattened bladelike portion of a leaf, as distinct from the petiole and leaf base. The shape of the lamina and the nature of its margin are important taxonomic characters (see illustrations). Leaf laminas are usually the main photosynthetic organs and are structured accordingly (see palisade mesophyll , spongy mesophyll ). They are placed so as to make the best use of incoming light with the minimum amount of either overlapping or wasted space. This is particularly evident in a tree canopy. The pattern so achieved is termed the leaf mosaic and is mainly a result of *phyllotaxis.

2. Any thin flat organ, such as a petal or the thallus of many macroscopic algae."

"Phyllotaxis (phyllotaxy) = The arrangement of leaves on a stem. In most plants the leaves are inserted singly and spirally on the stem. Sometimes two or more leaves are formed at each node giving an opposite or whorled arrangement (see illustration). The phyllotaxis of a given plant may be described by giving the angle of divergence between successive nodes. This varies between species but if many primordia are being formed it is normally not less than 137.5°, the so-called Fibonacci angle. Phyllotaxy may also be described by the *genetic spiral or by *parastichies. Many theories have been advanced to account for the regular nature of phyllotaxis (see available space theory, repulsion theory)." [In school we just learned Alternate: 1 leaf per node. Opposite: 2 leaves per node. and Whorled: 3+ leaves per node]

leaf and phyllode, (phyllode mcqbiology.com) and cladode and leaf and lamina and phyllotaxis <--- botanydictionary.org

..good info thanks Cosmic Spore..and well laid out..

as Phyllodes are extensions of the Petiole, they are in effect an extension of the stem bark..
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