There are many ways to describe a leaf in scientific terms. You can refer to the leaf's arrangement, shape, the shape of its edges, the way it is structured, the shape of the top of the leaf, the bottom of the leaf, whether it has a stem and how it feels. Using the proper scientific terminology when referring to leaves can help aid in the description of a plant.
A leaf that is simple has only one blade. A simple leaf may be stipulate, or have a small cuff at the bottom of the stem (scientifically, the leaf's terminal stem is called the "petiole"). An exstipulate leaf does not have a cuff, or stipule. A sessile leaf has no petiole or stem. Clasping base simple leaves directly hook onto the stem of the plant.
Compound leaves have more than one blade. Compound leaves can be palmately compound, with individual leaflets arranged in a spread out fashion much like the fingers radiating around your palm.
Pinnately compound leaves have leaflets arranged on either side of an individual leaf stem - called a rachis. Trifoliate leaves have three pinnately compound leaflets. A bipinnate leaf has multiple rachis with many leaflets arranged around a central plant stem. A pinnatified leaf is a compound leaf that appears almost shredded, like that of a fern.
Leaves may be arranged in three ways--alternately, opposite or whorled. Alternate leaves have only one leaf per leaf node, the spot where the leaf attaches to the stem. No two leaves match up on opposite sides of the stem. Opposite leaves are matched with one leaf per side of the stem, or two leaves per node. Whorled leaves are arranged with three or more leaves per leaf node.
Plant leaves can also be scientifically described by their shape. Cordate leaves are heart shaped. Obcordate leaves appear as an upside down heart, with the widest part of the heart at the base of the stem.
Linear leaves are long and skinny, while lanceolet leaves are long and blade shaped. Oblanceolate leaves appear as upside down lanceolet leaves. Oblong leaves appear as a stretched out oval with a rounded top edge. Elliptical leaves are an irregular oval appearing only slightly thinner at the top. Ovate leaves are oblong leaves that have a wide base and pointed top. Obovate leaves are the inverse of ovate leaves.
Spatulate leaves begin skinny, terminating at a large irregular oval near the top of the leaf. Cuneate leaves look like rounded upside down triangles. Falcate leaves are curved leaves that are skinniest near the terminus or node.
Aruculate leaves look like arrowheads with curled edges near the rachis. Hastate leaves look like triangles that have been pinched between each point. Deltoid leaves resemble the suit of spades in a deck of playing cards. Reniform leaves resemble kidney beans, while peltate leaves are circular in nature.
There are even special terms to define the edges, or margins, of leaves. An entire leaf margin is smooth and without interruption. Serrate leaf margins resemble a serrated kitchen knife. Doubly serrate margins are jagged in appearance. Serrulate leaf margins are those that are very finely serrated. Dentate leaves appear to have small squares taken out of the margin, while incised leaves look as though they have been chewed on by an insect or animal. Crenate leaves have a dainty half circles at their margins, while undulate leaves appear to roll or wave. Sinulate leaf margins have deep, oval grooves on the edges.
The coatings of leaves have a specific terminology as well. Glaucous leaves are covered in a white powder or wax. Farinose leaves feel gritty to the touch and may leave particles on your fingers when manually examined. Scurfy leaves feel scaly, while viscid and glutinous leaves are sticky. Punctate leaves are dotted with transparent pits, while papillose leaves are covered in raised dots. Tuberculate and verrucose leaves have large bumps. Rugose leaves are highly wrinkled, such as those in the mint family. Glaborous leaves are smooth, without any hairs or protuberances. Pubescent leaves are covered in hairs of any sort.