Thuja occidentalis

Sun, Bin, Cui, Yi-Ming, Wang, Hai-Feng, Ferguson, David K., Xiang, Qiao-Ping, Ma, Qing-Wen & Wang, Yu-Fei, 2015, Recognizing the species of Thuja (Cupressaceae) based on their cone and foliage morphology, Phytotaxa 219 (2), pp. 101-117 : 104

T. occidentalis

Seed cones narrowly ovate ( Fig. 2B ), 8–12 mm × 4–6 mm. Bract-scale complexes (3–) 4 (–5) pairs, the second whorl narrowly obovate, apex obtuse, base acute, umbo apex acute ( Fig. 2G ).

Facial leaves with obvious glands, lateral leaves with inturned apex, appressed to the facial leaves, no overlapping between the adjacent lateral leaves ( Fig. 2L ). Leaf apex obtuse without micro-teeth.

Almost no stomata on the abaxial surfaces of facial leaves, 2 triangular shaped stomatal bands on the proximal part of adaxial surface ( Figs. 3C, D ).

Subsidiary cells with low anticlinal walls, straight and continuous, margin denticulate (jagged), periclinal wall rough, the base of inner surface of papilla without thickening ( Figs. 5D , 9D , 11D ).

The inner surface of epidermal cells with low anticlinal walls, straight and continuous, margin with coarse particles, periclinal wall with coarse particles ( Fig. 11C ).

Figures

FIGURE 2. Characters of cones, bract-scale complexes and tip branches of Thuja. A, F, K, T. koraiensis; B, G, L, T. occidentalis; C, H, M, T. plicata; D, I, N, T. standishii; E, J, O, T. sutchuenensis.—Arrows pointing to the umbo; Scale bars = 2 mm.

FIGURE 3. The distribution of stomata on the abaxial and adaxial surfaces of facial leaves and the apex of facial leaves. A–B, T. koraiensis; C–D, T. occidentalis; E–F, T. plicata.—DFL: abaxial facial leaves; VFL: adaxial facial leaves; Scale bars: A, C, E = 0.5 mm; B, D, F = 0.1 mm.

FIGURE 5. The arrangement of stomata and subsidiary cells on the abaxial surface of facial leaves. A–B, T. koraiensis; C–D, T. occidentalis; E–F, T. plicata.—SC: subsidiary cell; FL: Florin ring; Scale bars: A, C, E = 50 μm; B, D, F = 10 μm.

FIGURE 9. Characters of the outer surface and inner surface of stomata on the abaxial surface of facial leaves. A–B, T. koraiensis; C–D, T. occidentalis; E–F, T. plicata.—FL: Florin ring; Pa: papilla; Scale bars = 20 μm.

FIGURE 11. Characters of the inner surface of epidermal cells in stomatal area and non-stomatal area on the abaxial surface of facial leaves. A–B, T. koraiensis; C–D, T. occidentalis; E–F, T. plicata.—IP: inner surface of papilla; Scale bars = 20 μm.