Simple and compound leaves
When the leaves have an entire margin, slightly affected or deeply cut, but not up to the middle rib, we speak of simple leaves (Betula pendula, Ostrya carpinifolia, Castanea sativa, Alnus glutinosa). If, on the contrary, the parts into which the sheet is divided become completely independent of the other, so much so that each can also be equipped with its own petiole, it is called a compound leaf (Robinia pseudoacacia).
The leaf (source Iprase Trentino)
The compound leaves are pinnate when the leaflets are arranged to the right and left of the rachis as in a pen and webbed if the leaves are arranged in a fan. The pinnate are learned if they have a terminal leaflet, otherwise they are pinned. The pinnate leaf can be twice (bipinned) or three times pinnate (tripennate). A leaf made up of only three leaves is said to be trifoliate (Trifoglio, Fragola).
Depending on the shape of the blade, there are filiform leaves (long and thin), needle-like, lesiniform (made with a awl, similar to a thin awl), linear (with an elongated and narrow blade), lanceolate, oblong (about two times longer than wide), oval, ovate, spatulate, elliptical, round ...
The images show only some of the many forms found in nature.
Some forms of foil
The ribs are formed by bundles of vessels and fibers for the transport of the lymph and also form the skeleton of the lamina. Depending on the arrangement of the ribs the leaf can be penninervia: with ribs arranged as in the feathers of birds (Carpinus betulus); parallelinervia: with almost parallel ribs as in Graminaceae; palminervia: with main ribs that all start from a single point (Acer campestre).
The margin: engraved leaves
Often the edge of the leaf has few but deep grooves that highlight protrusions called lobes. In these cases the leaf is called lobed. If the indentations reach about half the distance between the margin and the median rib, it is called a cracked leaf, left if instead they reach up to the median rib, sect (or sectioned) when the rib is reached. When the incisions are placed on the left and on the right of the main rib we speak of pinnate leaves; when instead they open like the fingers of a hand the leaf is palmatolobata. The pinnate leaf with acute lobes and straight inside is roncinata, if the upper lobe is much larger than the others it is said to be lirata.
The margin: leaves not engraved
As regards the shape of the margin, there are leaves with a full margin (if there are no incisions or protrusions), sinuous (with a wavy line), serrated (with sharp teeth facing towards the lamina of the lamina), toothed (with acute protrusions facing outwards ), doubly toothed (with large teeth in turn toothed), crenate (with protrusions with rounded contour). When the lamina folds down near the margin, we speak of lamina revoluta or margin revoluto, when instead it folds upwards, it is said to be involute at the margin.
Margin of leaves not engraved