Characters determining for sectional discrimination
1. arrangement
- alternate : a character very frequent in many sections of the Begonia genus
B. foliosa Kunth / Lepsia section / Colombia, Venezuela, Ecuador : alternate leaves
- opposite : a rare character in Begonia genus
B. subthorpioides Ridley / Heeringia section / Malaysia – Thailand : the upper leaves of this species are opposite
- distichous and close leaves : leaves are laid in two vertical rows in a same plane ; we often find that with creeping begonias
B. thelmae L.B. Smith & D.C. Wasshausen / section no determinate / Brazil : distichous leaves
- whorled or verticelate : sometimes on acaulescent plants (without a stem)
B. adenopoda Lemaire / Lauchea section / Myanmar : verticelate leaves
2. number
- 1 or 2 leaves
B. sambiranensis Humbert / Quadrilobaria section / Madagascar : only a leaf
- more than 2 leaves : most of begonias
B. minutifolia N. Hallé / Filicibegonia section / endemic from Gabon : many leaves
3. position relative to petiole
- straight : when the midrib of the blade is exactly a continuation of the petiole.
B. molleri Warburg / Tetraphila section / Sao Tomé : leaf straight, the midrib and the petiole are in alignment
- oblique : the petiole is at an acute angle (45°) to the midrib
B. sinuata Wallich / Parvibegonia section / Malaysia : oblique leaf, the petiole is at an acute angle (45°) to the midrib
B. horticola Irmscher / Tetraphila section / central Africa : oblique leaf, the petiole is at an acute angle (45°) to the midrib
- transverse : the petiole is at an right angle to the midrib
B. formosana Masamune / Platycentrum section / Taiwan : the petiole is perpendicular to the blade
4. symmetry
- symmetrical blade : rare in Begonia genus
B. horticola Irmscher / Tetraphila section / Congo – Zaïre – Uganda : blade almost symmetrical
- asymmetrical blade : common
B. silletensis CB Clarke subsp. mengyangensis Tebbitt / Sphenanthera section / China : strongly asymétrique blade
5. peltate or no peltate
- peltate leaf : the petiole is not attached to the margin but inside the blade.
B. microsperma Warburg / Loasibegonia section / Cameroun : peltate leaf
- no peltate : the petiole is attached to the margin of the blade
B. garagarana C de Candolle / Gireoudia section / Panama: no peltate
6. divisions
- simple leaves : the blade is not divided or lobed
B. mariannensis / Knesebeckia section / The Antilles (Trinidad) / simple leaf
- palmatilobed leaves : the blade is lobed or divided in a radial way (laid as the hand fingers) in lobes (divisions reach lessthan the middle of the blade)
B. China sp / section Diploclinium / China : palmatilobed leaves
- palmatifid leaves : idem but the divisions reach the middle of the blade ; a rare character in the Begonia genus
B. antsiranensis Aymonin & Bosser / Quadrilobaria section / endemic species from Madagascar : palmatifid leaves
- palmatisect leaves : divisions go past the middle of the blade
B. diadema Linden / Platycentrum section / Malaysia – Borneo : palmatisect leaves
B. pedatifida Léveillé / Platycentrum section / China : palmatisect leaves
B. mananjebensis Humbert / Quadrilobaria section / endemic from Madagascar : palmatisect leaves
- pinnatifid leaves : no palmate but pinnate (as the beards of a feather on both sides of the rachis) the divisions don’t reach the midrib
B. aspleniifolia Hooker f. / Filicibegonia section / endemic from Gabon : blade pinnatisect : pinnatifid, with divisions which go past the middle of the blade
- bipinnatifid leaves or more divided : when the pinnatifid divisions are themselves pinnatifid
B. bipinnatifida / Petermannia section/ new Guinea : bipinnatifid leaves
- compound leaves : the blade is divided in several (palmaty) lobes, each one has a petiole (leaflets) ; rare character in Begonia genus
B. hemsleyana J.D. Hooler / Platycentrum section / China : compound leaves
- filiform leaves : the blade is segmental
B. sp. Madagascar / Erminea section / Madagascar : filiform leaves divided in segments ; themselves are twice divided
7. nerves
- palmate nerves : laid as the hand fingers
B. sericoneura Liebmann / Gireoudia section / Central America : palmate venation
B. beccarii Warburg / Diploclinium section / Malaysia (Borneo : Sarawak) : palmate venation
- palmate-pinnate nerves : the first nerves are palmate and the next ones are pinnate
B. humilis Dryander / Doratometra section / from The Antilles to Peru and Brazil : palmate-pinnate nerves
- pinnate nerves : nerves are laid as the beards of a feather
B. aurilculata JD Hooker / Filicibegonia section / Gabon : pinnate nerves
B. ulmifolia Willdenow / Donaldia section / Guianian plateau : pinnate nerves
8. indument : characters no visible to the naked eye
- scales thin, dry and membranous outgrowths (trichomes) of epidermal origin : plants of Baccabegonia, Squamibegonia and Tetraphila sections and some species of the Loasibegonia section
- they can be more or less circular or stellate on some Asia and South America species of Knesebeckia and Pritzelia sections
Characters no determining for sectional discrimination
- petiole
- without petiole : sessile leaves
B. polygonoides JD Hooker / Tetraphila section / Tropical Africa : leaves nearly sessile
- glabrous or hairy :
B. picturata Y. Liu, S-M Ku & Ch-I Peng / Coelocentrum section / China (Guangxi) : petiole strongly hairy
B. roxburghii A. de Candolle / section Sphenanthera / Inde – Myanmar : glabrous petiole
2. blade shape
- cordate : heart-shaped, basally rounded with a deep notch
B. aliceclarckiae Ziesenhenne / Weibachia section / Mexico : cordate blade
- auriculate : with an auricle on the widest side of the blade and to the base
Gabon sp. nov / asymmetrical blade with an auricle to the base and cordate to the other side,
- obtuse to the base or the apex: rounded to the top or to the base
B. kisuluana Büttner / Tetraphila section / from Nigeria to Angola : obtuse leaves to the apex
- lanceolate : lance-shaped (the widest part to the base)
B. henrilaportei Scherberich & Duruisseau / Quadrilobaria section / Madagascar : linear-lanceolate blade, almost symmetrical, pinnatifid, incised.
B. komoensis Irmscher / Tetraphila section/ Equatorial Africa : lanceolate blade
- cuneiform base : wedge-shaped or triangle-shaped
B. maynensis A de Candolle / Knesebeckia section / Ecuador-Peru : lanceolate blade with a wedge-shaped base
- circular or subcircular :
B. atroglandulosa Sosef / Loasibegonia section / endemic from Gabon : blade almost circular
- falcate : sickle-shaped
B. poculifera JD Hooker / section Squamibegonia / Tropical Africa : falcate blade
3. blade appearance
- glabrous : smooth blade, without hairs
B. loranthoides var. loranthoides / Tetraphila section / EquatorialAfrica : blade upper surface glabrous and smooth
- pubescent or hirsute: blade with dense or sparsely hairs, short or long, spiniform, in diverse colors
B. sizemoreae R. Kiew / Platycentrum section / Vietnam : blade upper surface with long white hairs
B. limprichtii Irmscher / Platycentrum section / China : blade upper surface with sparsely spiniform hairs
- bullate : upper blade surface blistered
B. susaniae Sosef / Scutobegonia section / Cameroon – Gabon : bullate blade, each bubble with a spiniform hair
B. bullatifolia Kollmann / Knesebeckia sectin / Brazil (Espirito Santo) : bullate blade without hairs
4. margin :
- simple : the margin hasn’t any incision
B. erectocaulis Sosef / Scutobegonia section / Gabon : simple margin
- dentate : margin with teeth more or less large, more or less regular ; serrate if teeth are small
B. augustinei Hemsley / Platycentrum section / China : serrate margin with a larger tooth at the end of nerves.
- crenulate : margin with small rounded teeth
B. furfuracea JD Hooker / Tetraphila section / Cameroun – Bioko : crenulate margin
- ciliate : margin with more or less long hairs
B. jingxiensis D. Fang & Y.G. Wei var. mashanica / Diploclinium section / Chine (Guangxi) : ciliate margin
Bibliography :
- The sections of Begonia / J. Doorenbos – M.S.M. Sosef – J.J.F.E. de Wilde
- Begonias of Peninsular Malaysia / Ruth Kiew
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BEGONIACEAE, Edition 2 / Part I : Annotated Species List / Jack Golding