a bit of botany : 3 / leaves

 

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

 

  1. 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
  • BEGONIACEAE, Edition 2 / Part I : Annotated Species List / Jack Golding