Therorhodion

(Maximowicz) Small in N. L. Britton et al.

in N. L. Britton et al., N. Amer. Fl. 29: 45. 1914 ,.

Etymology: Greek theros, summer, and rhodeos, rose, alluding to flowering time and resemblance
Treatment appears in FNA Volume 8. Treatment on page 453. Mentioned on page 375, 455.

Shrubs, (rhizomatous). Stems erect to sprawling or procumbent; twigs rough, with simple, long-stipitate, glandular or eglandular hairs, with or without unicellular hairs, (older twigs without peglike projections). Leaves persistent or deciduous, alternate; petiole absent or nearly so; blade membranous to chartaceous, margins entire or obscurely serrulate, fringed with eglandular or glandular-hairs; (venation brochidodromous, reticulum clear). Inflorescences terminal, reduced racemes, (each flower in bract-axil); perulae green, leaflike proximally. Flowers bisexual, bilaterally symmetric; sepals 5, slightly connate; petals 5, connate ca. 1/3 their lengths, corolla deciduous, ± rotate; stamens 10, included, (unequal); anthers without awns, dehiscent by terminal pores; ovary 5-locular; style inserted in slight depression at ovary apex, (curved, long, slender); stigma capitate. Fruits capsular, ovoid, dehiscence basipetally septicidal. Seeds ca. 50–100, (brown), ± ellipsoidal, without appendages; testa smooth. x = 12.

Distribution

Alaska, ne Asia (ne China), ne Asia (Japan), ne Asia (Korea), ne Asia (Russian Far East)

Discussion

Rhododendron Linnaeus sect. Therorhodion Maximowicz, Mém. Acad. Imp. Sci. Saint Pétersbourg, Sér. 7, 16: 47. 1870; Rhododendron subg. Therorhodion (Maximowicz) Drude

Species 3 (2 in the flora).

Therorhodion is often included within Rhododendron; cladistic analyses (K. A. Kron and W. S. Judd 1990; Kron 1997) indicate that the group lies outside the Rhododendron clade, and it was given generic status by J. K. Small (1914), H. F. Copeland (1943), P. F. Stevens (1971), Kron et al. (2002), and Stevens et al. (2004).

Plants of Therorhodion from the Aleutian Islands and the southern coast of Alaska have leaves that lack or have only sparse stipitate-glandular hairs, and corolla lobes that are hairy outside. In contrast, plants from the Seward Peninsula and lower Yukon River valley have leaves that are obviously glandular-hairy and corolla lobes that are glabrous outside. These two morphological entities often have been recognized as varieties or subspecies (W. R. Philipson and M. N. Philipson 1986; E. Hultén 1927–1930, 1968); they do not intergrade (at least in North America) and are recognized here as distinct, allopatric species. The taxonomy of this group will remain tentative until the genus is revised using modern methods. The third species of the genus, T. redowskianum (Maximowicz) Hutchinson occurs in eastern Asia.

Selected References

None.

Key

1 Leaf blades (of vegetative branches) eglandular or sparsely glandular-hairy; outer corolla surface hairy, lobe margins ciliolate Therorhodion camtschaticum
1 Leaf blades (of vegetative branches) glandular-hairy; outer corolla surface ± glabrous, lobe margins smooth. Therorhodion glandulosum

"/3" is not declared as a valid unit of measurement for this property.

... more about "Therorhodion"
Kathleen A. Kron +  and Walter S. Judd +
(Maximowicz) Small in N. L. Britton et al. +
furrowed +  and smooth +
not flaky +
acicular;plane +
membranous;chartaceous +
rotate to crateriform campanulate cylindric globose or urceolate +
Alaska +, ne Asia (ne China) +, ne Asia (Japan) +, ne Asia (Korea) +  and ne Asia (Russian Far East) +
undifferentiated +
fusiform +
Greek theros, summer, and rhodeos, rose, alluding to flowering time and resemblance +
pendulous +  and erect +
unicellular +, eglandular +, glandular +, long-stipitate +  and simple +
terminal +  and axillary +
deciduous +  and persistent +
serrulate +  and entire +
parietal +, axile +  and placentation +
tenuinucellate +  and unitegmic +
reduced +
not sticky +
4-5-carpellate +
in N. L. Britton et al., N. Amer. Fl. +
reduced +
not +  and winged +
distinct +
ellipsoidal +
procumbent +  and sprawling +
creeping +  and sprawling +
peltate +  and capitate +
straight +
Undefined tribe Empetraceae +
Therorhodion +
Ericaceae subfam. Ericoideae +
achlorophyllous +  and chlorophyllous +
evergreen +, deciduous +  and perennial +
heterotrophic +, autotrophic +  and mycotrophic +