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trees of pyramidal habit and aromatic odour, belonging to the tribe Cupressineæ of the order Coniferæ. Branches spreading and much ramified, terminating in so-called "branch-systems," which are flattened in one plane and are 2-, 3-, or 4-pinnately divided, their primary and other axes being densely clothed with scale-like leaves. These branch-systems when they fall are cast off as a whole, the leaves not falling separately. The leaves, which are minute, are more or less coalesced with the axes, on which they stand in 4 ranks in 2 decussate pairs, those of the lateral ranks being conduplicate or boat-shaped, those placed dorsally and ventrally being flattened. In the seedling stage and certain horticultural varieties, the foliage is different, the leaves being acicular, spreading, and uniform; all 4 ranks in this case are alike.

Flowers monœcious, all solitary and terminal on the ultimate short branchlets of the preceding year, the male and female flowers on different branchlets, the former on the branchlets near the base of the shoot, the latter on those near its summit. Male flowers cylindrical or globular, consisting of 3 to 6 pairs of stamens placed decussately on an axis, each with an orbicular connective bearing 2 to 4 pollen sacs. Female flowers minute cones, composed of opposite scales in which no distinction of ovular scale and bract is visible, continuous in series with the leaves at the end of the branchlet, 2 to 4 pairs in Biota, 4 to 6 pairs in Euthuya, mucronate at the apex, some sterile, the others fertile and bearing 2 to 3 ovules.

Cones solitary, ultimately deflected, except in Biota, in which they retain the erect position, oblong, ovoid, or almost globose, composed of 3 to 6 pairs of decussate scales, which are not peltate, some fertile, the others sterile, the uppermost often united together. Seeds 2 to 3 on each fertile scale. Cotyledons 2.

The genus Thuya, as understood here, does not include Chamæcyparis and