Lourtella, a New Genus of Lythraceae from Peru

Abstract

A new genus and species of Lythraceae, Lourtella resinosa, is described from Dpto. La Libertad, Peru. It is unique in the family by possessing globose, spiny to spinulose trichomes, discontinuous nectaries, and especially by conspicuous secretory ducts in the stem and pedicel. Floral morphology and anatomy, pollen morphology, and leaf and stem anatomy are detailed. Lourtella is allied to a cluster of four genera, Adenaria, Koehneria, Pehria, and Woodfordia, but the presence of secretory ducts, together with the deviating nature of its globose trichomes and other apomorphies, isolate it within the group. Among recent specimens of Lythraceae sent to the first author for determination was a remarkable, previously unknown member of the family, collected in 1974 from a remote region of northern Peru. The specimen was unquestionably lythraceous as attested to by a large combination of characters: opposite, entire leaves; cymose, bracteolate inflorescences; actinomorphic, campanulate, 4-merous, perigynous flowers with valvate lobes and crinkled, pinnately-veined petals; stamens inserted at mid-level on the inner surface of the floral tube, the anthers dorsifixed with a narrow connective; ovary with reduced septa and fleshy axile placenta; seeds numerous, small, and obpyramidal. Young parts of the plant were coated with copious, resin-like secretions, a feature never before observed in any member of this family. The collection is the basis for description of the new genus and species of Lythraceae, Lourtella resinosa S. A. Graham, P. Baas & H. Tobe. Studies of floral morphology and anatomy, pollen morphology, and leaf and wood anatomy are presented for the collection to confirm the familial position of the plant and to allow detailed comparison with similar, recently published data from other lythraceous genera (Baas 1986; Baas and Zweypfenning 1979; Graham and Lorence 1978; Graham et al. 1986). TAXONOMY Lourtella S. A. Graham, P. Baas & H. Tobe, gen. nov.-TYPE: Lourtella resinosa S. A. Graham, P. Baas & H. Tobe, sp. nov. Fam. Lythraceae. Frutex arborescens ramis oppositis, brevibus, rigide divaricatis; rami juniores folia inflorescentiaque pilis globosis minutis obsiti, medulla caulis orificio secretorio centrali, cortex orificiis secretoriis perforatis. Folia decussata, subcoriacea, oblonga, petiolata. Dichasia 3(4)-flora, axillaria, bracteis bracteolisque persistentibus. Flores 4-meri, homoeostyli, perfecti; appendices 0. Petala 4, alba, tubo aequilonga vel longiora. Stamina 8, ad tubi 1/3_ 1/2 inserta, uniseriata, episepala ceteris vix longiora; antherae tetrasporangiferae, dorso affixae, connectivo parvo. Pollinis grana prolata, 3-colporata; exinio minute verrucato, grano amplitudo parva. Ovarium sessile, globosum, 2-loculare; dissipimenta ovarii fructusque tenerrima; placenta pyriforma vel subglobosa. Nectarium inter basim floris et staminorum locatum, interruptum. Capsula inclusa, tenuissime membranacea, ad apice irregulariter rumpens. Semina circ. 50, obpyramidata, 1 mm longa. Ab Pehria differt orificiis secretoriis caulis pedicellisque, pilis globosis spinulosis, petalis albis, ovario non-stipitatio, nectariis interruptis.