Published In:
Botanical Journal of the Linnean Society 187: 386. 2018. ( Bot. J. Linn. Soc.)
(Last Modified On 4/8/2021)
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Acceptance
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Accepted
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Note
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Tribe Chiococceae
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(Last Modified On 9/15/2021)
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Notes
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Motleyothamnus includes one woody species found in found in dry valleys high in the Andes. This species has medium-sized to small leaves that sometimes have small pubescent domatia; short, triangular, persistent interpetiolar stipules; 5-merous flowers borne in rounded cymes on the apices of the main stems; calyx limbs lobed nearly to the base; salverform, white, medium-sized (1.5-2.5 cm) corollas with lobes that are about as long as the tube and thinly imbricated in bud; slender, long-exerted anthers and style; and ellipsoid, somewhat flattened and didymous, somewhat small, functionally septicidal capsules with several flattened, marginally winged, medium-sized (ca 3 mm) seeds. The plants vary from glabrous to puberulous or pilosulous. Motleyothamnus corymbosus grows as rather small shrubs to trees at least 12 m tall (Valenzuela 2775, MO). The stems are usually markedly lenticellate. The leaves vary in size among different plants, and from petiolate to subsessile. Paudyal et al. (2018) described the leaves as sometimes ternate, but this has not been seen in this study. The stipules were described by Paudyal et al. (2018: 386) as lacking colleters or with these present but "inconspicuous". However, on the specimens studied the stipules have well developed abaxial colleters that often are large enough to extend past the margins.
The corollas of Motleyothamnus corymbosus are white at anthesis, and then apparently become yellowed with age. This pattern is common in noctural flowers, and this plus the strong sweet floral fragrance described in collection notes suggest this species may be nocturnal. The corolla lobes are narrowly ligulate, about as long as the tube, and spreading to strongly reflexed at anthesis. These lobes are asymmetrically oriented on dried specimens, and appear to usually have one lobe only weakly spreaing and perhaps held at the top of the flower and the other lobes strongly spreading. One collection (Stork & Horton 10409, MO) described the flowers of Motleyothamnus corymbosus as similar to those of Lonicera (Caprifoliaceae) in fragrance and form, which also suggests that the flowers are similarly zygomorphic in orientation of the corolla lobes and perhaps stamens at anthesis.
Motleyothamnus corymbosus is probably at least sometimes deciduous. The size of the leaves, flowers, and fruits varies markedly among the specimens, and these plants may deserve further study as to whether there is more than one species. However, such size variation is not uncommon among plants growing in seasonal environments that receive varied amounts of rainfall and soils with limited nutrients, such as dry Andean valleys. Marked variation in flower and fruit size is often found among specimens from the same area.
Motleyothamnus is similar to Coutareopsis, and especially Coutareopsis andrei, and these are frequently confused. The similarity of these was noted by Taylor & Lorence (2010: 96, as Coutarea and Exostema), who noted that Motleyothamnus differs in its stems with regularly developed internodes and its salverform corollas with the lobes as long as or longer than the tube, vs. stems usually with short-shoots and funnelform to tubular corollas in Coutareopsis. Motleyothamnus corymbosus was previously known to not be closely related to the other species of Exostema (McDowell & Bremer, 1998), but Exostema and related genera and species were not well enough known to present a well supported different classification (Taylor & Lorence, 2010).
The molecular study of Exostema and related genera by Paudyal et al. (2018) found Motleyothamnus and Coutareopsis as sisters on a monophyletic clade, and separated them taxonomically. According to their explicit taxonomic criterion (2018: 375), separation of a monotypic genus required an autapomorphic morphological character that distinguished it; however, Paudyal et al. cited no specific morphological character for their Motleyothamnus. They did outline its separation from some other genera in the analysis, but some of of their distinctions are not entirely clear. They regarded (2018: 379) the corolla form of Motleoythamnus as different from that of Coutareopsis, and this may have beeen the autoapomorphy used to separate it; however, they also stated, in their immediately preceding sentence here, that they considered the corolla form of Motleyothamnus to be the same as that of Coutareopsis coutaportloides and gave no other morphological differences between these genera. Their formal diagnosis of Motleyothamnus as a new genus contrasted it only with Solenandra, which was not found to be closely related in their analysis (this may have been because Solenandra included some species formerly included in Exostema, the genus in which Motleyothamnus corymbosus was previously treated, but the particular reason for separating Motleyothamnus formally only from Solenandra was not explained). Paudyal et al. did outlines their separation of Coutareopsis from Motleyothamnus (2018: 379) in another part of the text, where they distinguished Coutareopsis by its "1- to 3-flowered inflorescences on short-shoots" in contrast to cymose, multi-flowered, terminal inflorescences in Motleyothamnus. However, Coutareopsis coutaportloides has inflorescences that are usually terminal on the main stems and its plants usually lack short-shoots, in spite of the overall characterization by Taylor & Lorence (2010). Given the molecular placement of Coutareopsis and Motleyothamnus as forming a monophyletic group, the range of corolla forms and colors already included in Coutaropsis, the sympatric range of these, and the inaccurate analysis of the characters of Coutareopsis that were used to separate these genera, Motleyothamnus cannot be regarded as a strongly distinct genus.
The clade comprising Coutareopsis and Motleyothamnus was found by Paudyal et al. (2018) as sister to the clade comprising Coutarea and Adolphoduckea, and this combined clade was found by them as sister to a clade comprising Exostema and Solenandra. In their formal description of Motleyothamnus, Paudyal et al. (2018: 386, diagnosis) distinguished it only from Solenandra in spite of these other more closely related genera. Motleyothamnus was separated based on its strongly laterally compressed capsules (vs. "terete or slightly laterally compressed" in Solenandra), "trapezoidal placenta" (vs. "hemiellipsoidal placenta"), and "acrobasipetal seed arrangement" (vs. "acropetal, centripetal, or basipetal seed arrangement"). The "trapezoidal" placenta with the seeds "vertically imbricate, acrobasipetally arranged" they described (2018: 386, genus description) appears to correspond to the laminar placenta with the ovules variously pendulous and ascending of Aiello (1979).
Author: C.M. Taylor.
The content of this web page was last revised on 8 April 2021.
Taylor web page: http://www.mobot.org/MOBOT/Research/curators/taylor.shtml
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Distribution
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Dry forest and scrub, often on sandstone or limestone, 820-2574 m, Andes of Peru (Cajamarca, Cusco, Huancavélica, Junín, La Libertad, Pasco).
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References
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- Taylor, C. M. & D. H. Lorence. 2010. Rubiacearum americanarum magna hama pars XXII: Notable new species of South American Coutarea, Morinda, Patima, and Rosenbergiodendron. Novon 20(1): 95–105.
  - Paudyal, S.K., P. G. Delprete, S. Neupane & T. J. Motley. 2018. Molecular phylogenetic analysis ad generic delimitations in tribe Chioccceae (Cinchonoideae, Rubiaceae). Bot. J. Linn. Soc. 187: 365-396.
- McDowell, T. & B. Bremer. 1998. Phylogeny, diversity, and distribution in Exostema (Rubiaceae): implications of morphological and molecular analyses. Pl. Syst. Evol. 212(3–4): 215–246.
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Shrubs and small to medium-sized trees, unarmed, terrestrial, without raphides in the tissues. Leaves opposite, subsessile to petiolate, entire, with the higher-order venation not lineolate, sometimes with pubescent domatia; stipules intepetiolar, triangular, erect and perhaps imbricated in bud, persistent. Inflorescences terminal, cymose, several- flowered, pedunculate, bracteate. Flowers pedicellate, bisexual, homostylous, protandrous, medium-sized, fragrant, perhaps nocturnal; hypanthium ellipsoid and flattened; calyx limb developed, deeply 5-lobed, without calycophylls; corolla salverform, white, medium-sized (1.5-2.5 cm), pilosulous to puberulous inside, lobes 5, narrowly ligulate, about as long as tube, thinly imbricated (quincuncial) in bud, spreading to reflexed perhaps asymmetrically at anthesis, without appendages; stamens 5, inserted at base of corolla tube, filaments thickened and coherent at base, anthers narrowly oblong, basifixed, dehiscent by linear slits, exserted, shortly sagittate at base, without appendage at top; ovary 2-locular, with ovules several in each locule, on axile laminar placentas with ca. 4 ovules ascending and ca. 4 ovules pendulous, stigma shortly biblobed, exserted. Fruit capsular, ellipsoid to obovoid, laterally flattened and weakly didymous, shallowly loculicidal then deeply septicidally dehiscent from apex with valves apparently remaining fused at base, woody, smooth, without lenticels, with calyx limb persistent; seeds several per locule, discoid, flattened, medium-sized (ca. 3 mm), with concentric wing, marginally thickened, entire, densely foveolate-reticulate.
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