Luzula johnstonii Buchenau
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Authority
Ebinger, John E. 1964. Taxonomy of the Subgenus Pterodes, Genus Luzula. Mem. New York Bot. Gard. 10 (5): 279-304.
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Family
Juncaceae
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Scientific Name
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Description
Species Description - Perennial; rhizomes and stolons present, these similar, to 10 cm long, 1-4 mm wide, with purplish scale-like leaves and slender adventitious roots; blades of the basal leaves flat, 3-7 mm wide, to 20 cm long, margins sparsely pubescent, apex mueronate acuminate or callose-tipped; culms erect, slender, smooth, 20-40 cm tall, bearing 2-4 leaves; sheaths closed, pubescent at the throat with long white hairs, blades linear, 3-6 mm wide, to 9 cm long, margins sparsely pubescent, callose-tipped; inflorescence terminal, decompound; pedicels erect to slightly spreading, never reflexed; basal bract erect, much shorter than the inflorescence, leaf-like, green to purple, the margins sparsely pubescent, callose or mucronatetipped; other bracts purple, shorter; inner bract at the base of each pedicel usually truncate with a hyaline tip, sometimes pubescent; outer bracts usually longer than the inner, tip acuminate, sometimes extended into a slender hair-like tip; bracteoles ovate-lanceolate, acuminate, awned, purple with hyaline maro-ins, shorter than the flowers; perianth segments similar, equal, lanceolate, entire, usually awned or the petals frequently unawned, purple with narrow' hyaline margins, 3-4.5 mm long; stamens shorter than the perianth, filaments linear white, anthers linear usually shorter than the filaments; pistil erect, ovary trigonous, style filiform 1 mm long, stigmas 3 erect 2-3 mm long; fruit equalling the perianth or shorter, apex extended by the persistent base of the style, usually light purple (sometimes stramineous); seeds 1.5 mm long, purple to black; caruncle at apex, erect, obtuse, 0.4 mm long or less.
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Discussion
Luzula johnstonii Bucljenau, Bot. Jahrb. 12: 79. 1890.
Juncoides johnstonii (Buchenau) O. Ktze. Eev. Gen. PL 2: 724. 1891.
Type. H . H. Johnston 28, collected in 1884 in Kenya on Mt. Kilimanjaro at an elevation of 8000-9000 feet. (K.)
Hybrids. Because this species is geographically isolated, no naturally occurring hybrids have been found.
Luzula johnstonii is found only in the high mountainous regions of Kenya, Uganda, Ethiopia, Tanganyika and the Belgian Congo (Fig. 3). All of the material studied was collected at an altitude above 8,500 feet principally on Mt. Elgon, Mt. Kenya, Mt. Kilimanjaro and Mt. Ruwenzoi. A s a result of this mountainous habitat the populations growing on different mountains are separated from each other, and there is, accordingly, little or no opportunity for interbreeding. Even considering this lack of gene flow the species is uniform and most of the variation that takes place is in flower size and the amount of coloration of the perianth segments. This slight variation is usually found in plants from different mountains, but sometimes occurs in a population from a single mountain.
Morphologically this species is distinct from the other members of the subgenus. The caruncle in Luzula johnstonii is very short and obtuse while in the other taxa of the subgenus the caruncles are much larger. Probably the most distinctive feature of this species is the decompound inflorescence. No other member of the subgenus Pterodes consistently has a decompound inflorescence, but it is occasionally found in L. plumosa var. reflexa. Moreover, the nearly erect pedicels of L. johnstonii are found only in L. plumosa var. plumosa and L. forsteri.
Because of its distinct morphology and its disjunct distribution, this species has never been confused with any other member of the subgenus. Moreover, because of its uniformity no new specific epithet has been used for this species since it was described by Buchenau (1890). Furthermore, no varieties have been described. The only nomenclature change that has been made was when Kuntze (1891) transferred the species to the genus Juncodes because he considered this generic name to be the valid name of the genus.
Although many morphological features separate this species from the others in the subgenus, Nordenskiold (1957) discovered that Luzula johnstonii will form hybrids with most of the subgenus Pterodes. In these breeding experiments L. johnstonii was crossed with the North American species L. acuminata and the Asian species L. plumosa and sterile F1 hybrids were obtained. Crosses between L. johnstonii and the European species L. luzulina, L. forsteri, and L. pilosa resulted in partially fertile F1 hybrids and some F2 plants were even obtained. Evidently, then, L. johnstonii is most closely related to the European members of the subgenus. Its morphological characters also resemble those of the European species more than any other members of the subgenus.