Pinacea e: More on Morphology
The Pinaceae are best distinguished from other conifers, or plants in general by these characteristics: characteristics of the bark, branching patterns, types of shoots, characteristics of the leaves, and qualities of the reproductive structures. Most adult plants are of medium to large size, i.e. maximum height being about 100 meters tall. The maximum ages of these plants range from 1000 years or more to ages of several millennia. Pinaceae are mostly evergreen trees or shrubs that yield resin, a viscous substance.
The bark is either thin or thick, and scaly. Most of the genera have resin canals or tracheids. The distance between branches is determined by the length of the internodes. The growth is rhythmic with seasonal rest periods. The branches are horizontally spreading. Higher order branches tend to be more flexible, some of which droop. The maximum order of branching is 5-6. Shoots come out of the genera have long shoots, which separate stems and branches into internodal segments. Some genera (Cedrus, Larix, Pseudolarix) form secondary short shoots from the long shoots. Only Pinus has dwarf shoots, which bear needle-shaped leaf bundles. Pinus forms dwarf shoots in the axils of the bracts in the tree.
All leaves of Pinaceae are aromatic. Most are evergreen, with some others being deciduous like the Pseudolarix and Larix. Also, they are mostly linear and flattened. They are spirally arranged on shoots, and appear to be arranged in whorls on shorter shoots. Most of the flattened leaves are hypostomatic, with the stomata on the abaxial side. Picea and Pinus, though, are epistomatic, with the stomata on the adaxial side. The stomata are placed in lines and are usually covered with a whitish wax. Most of the genera have resin ducts in the mesophyll, or spongy tissue, of the leaf.
Male strobili, or cones, are solitary in most genera, but others are clustered. Most of the cones are similar among the Pinaceae. There are numerous microsporophylls, arranged in spirals. Each of these microsporophylls has two pollen sacs on the abaxial, or underside. The young cones are purple or red, and then turn yellow once the pollen is dispersed. Ovules, or female cones, develop on most of the outer branches, predominantly in the upper part of the crown. They consist of spirally arranged bracts and scales with a pair of seeds on the adaxial, or top side. Seeds are usually winged, but there are also cup-type shapes. Female cones are, for the most part, situated as erect at the crown, but some species have cones that start out as erect and become pendulous through time. All species of Pinaceae are monoecious, meaning that the male and female cones appear on the same plant. Sometimes, the male and female cones may occur in alternating years.
For more pictures of different species of Pinaceae, see Vascular Plant Image Gallery (Pinaceae).
Sources:
Dallimore, William. A Handbook of Coniferae including Ginkgoaceae. London: Edward Arnold & Co., 1923.
Farjon, Aljos. Pinaceae, drawings and descriptions of the Genera Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, Tsuga, Cathaya, Pseudotsuga, Larix, Picea. Koenigstein, Federal Republic of Germany. Koelto Scientific Books, 1990.
