A note about keys in general and the following key in particular:
Keys are identification devices that use the contrasting characteristics of the included organisms to partition the universe of potential identifications into successively smaller and smaller subgroups until, ultimately, the user reaches a name that should be applicable to the specimen at hand. A solid understanding of the morphology and descriptive terminology of the unknown organism is a necessary prerequisite for successful keying of unknowns. Further, it is critical that the key in use be appropriate to the task at hand, i.e., that it pertain to the correct taxa in the proper geographic context. The following key, for example, was designed primarily as a class exercise for biology majors to identify conifers in winter condition found on the University of Richmond campus. Thus, it includes a mixture of species native to central Virginia, USA, as well as exotic species from other temperate regions that are cultivated in the mid-Atlantic states. The intent is to emphasize diversity at the genus level. However, monotypic genera are identified to species, as are those for which only a single species is likely to be found in the region. Additional keys, such as those found in the references cited, will be required to identify species of several of the genera included here.
General Key:
A. Leaves (and in some, branchlets) deciduous, plants leafless in winter
B. Branchlets short and stubby (spur shoots), persistent; leaves 3-7 cm long............................ .................................................................................. Pseudolarix amabilis, Golden Larch
BB. Branchlets elongate and deciduous with the leaves deciduous; leaves < 3 cm long
C. Leaves (and leaf scars) alternate ...........................Taxodium distichum, Bald Cypress
CC. Leaves (and leaf scars) opposite ..... Metasequoia glyptostroboides, Dawn Redwood
AA. Leaves evergreen
D. Leaves distinctly elongate, linear, or needle-shaped and well-separated from the stem
E. Leaves in fascicles of 2, 3, or 5, enclosed in a papery basal sheath ........... (Pinus, Pine)
EE. Leaves not fascicled, not sheathed
F. Leaves alternate
G. Shoots markedly dimorphic, leaves on spur shoots appearing tufted ..................................................................................... (Cedrus, Cedar)
GG. Shoots uniform, leaves not born in tufts
H. Leaves distinctly flattened
I. Petiole and leaf blade distinct, or the leaf base obviously narrowed at attachment to node
J. Cones absent, seeds solitary; leaves uniformly green to yellowish green
K. Leaves less than 2.5 cm long, mature ovules less than 1.5 cm in diam., partially enclosed in a fleshy red aril ........ (Taxus, Yew)
KK. Leaves more than 2.5 cm long, mature ovules 2-3 cm long, without prominent aril.............Cephalotaxus harringtoniana, Plum Yew
JJ. Cones present, pendulous, with multiple seeds, leaves with two white stripes on the lower surface ............. Tsuga canadensis, Canada Hemlock
II. Petiole absent, leaves essentially sessile, not narrowed at point of attachment to stem
L.Cones pendulous; cone scales persistent; leaves 3-7 cm long ........ Cunninghamia lanceolata, China Fir
LL.Cones erect, cone scales deciduous at maturity; leaves mostly < 3 cm long ..................................... (Abies, Fir)
HH. Leaves round or square in xs, not flattened
M. Cones globose, ca 1.5 - 2.5 cm in diam, leaves curved apically ................................................ ..Cryptomeria japonica, Sugi, Japanese Cedar
MM. Cones elongate, more than 5 cm long, leaves more or less straight and divergent from the stem
N. Bracts hidden between cone scales, leaf scars prominent and peg-like ................................ (Picea, Spruce)
NN. Bracts prominent, 3-lobed, well exserted between cone scales, leaf scars only slightly raised, oval ............ Pseudotsuga menziesii, Douglas Fir
FF. Leaves opposite or whorled
O Leaves <2 cm long, often intermixed with scale-like leaves, cones soft and berry-like .................................................... (Juniperus, Juniper)
OO. Leaves >7 cm long, uniform and clustered towards the ends of the branches, cones woody ............. Sciadopitys umbellata, Umbrella Pine
DD. Leaves not especially elongate, scale-like and closely appressed to the stem
P. Branchlets flattened and forming flat fan-like sprays
Q. Cones elongate
R. Foliage aromatic, cone scales 8-12 ............... (Thuja. Arbor Vitae)
RR. Foliage not aromatic, cone scales 4-6 .................................. ............................................. Calocedrus decurrens, Incense Cedar
QQ. Cones globose
S. Leaves with white lines on underside; cones maturing in one growing season ............................ Chamaecyparis pisifera. Sawara Cypress
SS. Leaves uniformly dark green; cones maturing in two growing seasons, but seldom present on young plants ..................................................... ............................... XCupressocyparis leylandii, Leland Cypress
PP. Branchlets rounded or equally 4-angled and forming 3-d clusters not at all fan-like
T. Cones soft and berry-like, needle leaves (juvenile) and scale leaves (adult) often mixed...................................................................................(Juniperus, Juniper)
TT. Cones woody, leaves uniformly scale-like ..................... (Cupressus, Cypress)
The key presented above is adapted from materials contained in the following sources:
Bailey, L. H. 1951. Manual of Cultivated Plants. Macmillan Publishing Co., Inc. New York
Elias, T. S. 1980. The Complete Trees of North America. Van Nostrand Reinhold Company. New York.
Vidakovi, M. 1982. Conifers Morphology and Variation. Grafiki Zavod Hrvatske, Croatia. [transl. By M. oljan, 1991]