I wrote this key for the Trees and Shrubs Online Buddleja Page, sponsored by the John Spedan Lewis Foundation, and it is reproduced here with their permission. Only the species hardy or almost hardy in the UK are included, and the tender species excluded. Most species have pop-up images.
|1a||Leaves alternate.||Buddleja alternifolia|
|2a||Leaves very narrowly oblong, 10X or more as long as wide, corolla white, disc-shaped, 12-15m diameter.||B. virgata|
|2b||Leaves ovate, lanceolate, elliptic or somewhat triangular.||3|
|3a||Flowers yellow or orange, arranged in tight spherical heads.||4|
|3b||Flowers not arranged in spherical heads.||7|
|4a||Leaves small, densely tomentose on both surfaces, ovate with crenate margin; inflorescence a terminal spherical head of brownish orange flowers subtended by pair of leafy bracts.||B. marrubiifolia|
|4b||Leaves large, lanceolate, inflorescence composed of 3-7 spherical heads.||5|
|5a||Leaves subcoriaceous, upper surface glabrous, undersides conspicuously white tomentose, flowers burnt orange.||B. megalocephala|
|5b||Leaf upper surface somewhat rugose, flowers yellow or orange.||6|
|6a||Leaves large, lanceolate, upper surface rugose. Inflorescence a false raceme of 5-7 spherical heads, flowers yellow to orange.||B. globosa|
|6b||Underside of leaves, branchlet and buds more tomentose than in (4a) B. globosa, leaves also narrower and connate at base, flowers bright orange.||B. araucana|
|7a||Stamens exserted from corolla tube on filaments.||8|
|7b||Stamens held in throat or within corolla tube, sessile or with only very short filaments.||13|
|8a||Stamens fully exserted on long filaments.||9|
|8b||Stamens slightly exserted on short filaments.||10|
|9a||Corolla yellow, stamens also yellow, well exserted from throat. Leaves glaucous, triangular-ovate, irregularly dentate to crenate.||B. glomerata|
|9b||Corolla white, stamens well exserted from throat. Leaves narrow, willow-like.||B. saligna|
|10a||Leaf blade narrowly elliptic, upper surface bullate; inflorescence congested, corolla white with a wide golden-orange throat; stamens slightly exserted.||B. loricata|
|10b||Leaves ovate, cordate or elliptic, sinuate-lobed, petiolate, rugose and bullate above; flowers sessile, in glomerules. Corolla white, greenish or yellow-orange, corolla tube very short, 1.5-2.5mm long; stamens slightly exserted.||11|
|11a||Flowers white, greenish white or cream, indument on lower surface appressed.||B. cordata subsp. tomentella|
|12a||Flowers yellow-orange, indument on lower leaf surface usually thick and floccose, sometimes appressed. Inflorescences as long or longer than average leaves||B. cordata subsp. cordata|
|12b||As (12b) B. cordata subsp. cordata, but inflorescences half the length of average leaves.||B. cordata subsp. ovandensis|
|13a||Corolla tube with significant curvature, 10-20mm long||14|
|13b||Corolla tube straight.||16|
|14a||Branchlets terete, pubescent to tomentose. Leaves ovate, margin sub-entire, tomentose above, densely tomentose beneath. Inflorescence usually a horizontal panicle. Corolla purple to mauve-blue.||B. curviflora|
|14b||Branchlets quadrangular, less conspicuously pubescent.||15|
|15a||Branchlets quadrangular to sub-quadrangular, sometimes narrowly winged. Leaves ovate-acuminate, glabrous and sometimes glossy above, rusty pubescent beneath; inflorescences pendulous panicles, corolla purple.||B. lindleyana|
|15b||Branchlets quadrangular and widely four-winged. Leaves narrowly elliptic, acuminate at the apex, margin repand-dentate to subentire, glabrous above, sparsely pubescent to almost glabrous beneath. Inflorescence more upright on opening than in (15a) B. lindleyana. Corolla lavender or violet.||B. japonica|
|16a||Leaves large, elliptic and acuminate. Inflorescence lax; large corolla pink or wine-red, 1.5-2.5cm diameter, 20-30mm long, 6-9mm wide at throat, stamens and stigma in throat.||B. colvilei|
|16b||Corolla 1cm or less in diameter, opening at throat 5mm or less.||17|
|17a||Corolla orange, tube cylindrical, 28-48mm long, stamens in throat, leaves sub-coriaceous, elliptic to lanceolate.||18|
|17b||Corolla tube less than 20mm long.||19|
|18a||Corolla tube 28-34mm long, calyx lobes acute.||B. speciosissima|
|18b||Corolla tube 39-48mm long, calyx lobes acuminate.||B. longiflora|
|19a||Corolla small, lobes erect, corolla generally less than 6mm diameter.||20|
|19b||Corolla diameter generally greater than 6mm.||23|
|20a||Leaves elliptic to ovate, acuminate at apex, upper surface dark green and glossy, underside whitish. Inflorescence many flowered panicle, flowers sweetly scented, corolla white or cream with orange throat, lobes small less than 2.0 x 2.0 mm, tube 5.5-9.0 mm long, 1.2-2mm dimeter; anthers inserted well above the middle of the corolla tube.||B. auriculata|
|20b||Leaves not glossy or shiny on upper surface.||21|
|21a||Leaf blades narrowly elliptic, apex acuminate, undersides stellate-tomentose. Inflorescence terminal and spiciform; corolla small, mostly white without a conspicuous yellow throat, lobes erect, corolla tube 2.5-4.8 mm long and mostly less than 1mm diameter; stamens inserted above middle of corolla tube.||B. asiatica|
|21b||Inflorescence long and narrow thyrsoid cyme. Corolla pale lilac, mauve or pink, usually with a yellow throat. Stamens inserted in or near the mouth.||22|
|22a||Leaf upper surface glabrous, mid-green, underside only minutely stellate-tomentose. Branchlets rounded terete. Inflorescence terminal, narrow and cylindrical thyrsoid cyme. corolla small, pale lilac or pink, corolla tube 4-6.5 mm long, widening slightly towards the mouth, exterior glabrous or glabrescent, stamens inserted at or just below the mouth.||B. albiflora|
|22b||Leaf upper surface with some stellate hairs, lower surface tomentose. Branchlets four-angled and narrowly winged. Inflorescence cylindrical, thyrsoid cyme. Corolla small, usually less than 6mm diameter. white, lilac or purple, corolla tube 4-6 mm long, exterior tomentose, stamens inserted somewhat below the mouth.||B. myriantha|
|23a||Leaf blade triangular to somewhat ovate, margins crenate, dentate or shallowly lobed; both surface densely tomentose, upper surface occasionally glabrescent. Corolla pale lilac, pink or violet, exterior tomentose.||24|
|23b||Leaves ovate or elliptic.||25|
|24a||Leaves generally more than 6cm in length. Inflorescence spicate or paniculate cymes. Pistil length more than 4mm on average.||B. crispa
||More compact growth habit than in (24a) B. cripsa. Leaves small,
generally less than 5cm in length. Inflorescences a terminal thyrse,
few flowered. Pistil length less than 4mm on average.
||Leaves sage-like, connate or with leafy stipules, upper surface
rugose and bullate, underside tomentose with very prominent venation;
inflorescence paniculate, flowers sweetly scented, corolla blue, lilac
or white, tube 4-7mm long, anthers on short filaments inserted
approximately in middle of the tube.
||Leaves petiolate and not sage-like.
||Corolla diameter roughly 7 - 10mm. Diameter of corolla tube 3.0 mm
or more. Leaf blades narrowly ovate, apex acuminate, branchlets
four-angled, often winged.
||Diameter of corolla tube narrow, 3 mm or less.
||Calyx, exterior of corolla tube and ovary glabrous, or ovary
sparsely tomentose towards upper half. Corolla white, pink or purple.
Corolla tube sometimes widening towards the mouth, 5-8mm long, only
slightly longer than pistil, stamens at mouth and level or almost with
||Calyx, exterior of corolla tube and ovary tomentose to densely
tomentose. Corolla white, pink, maroon or purple. Corolla tube
cylindrical, much longer than pistil, stamens at mouth and placed
significantly above the stigma.
||Leaf blade narrowly ovate to elliptic, upper surface with
spreading hairs; margin serrate to crenate, apex acuminate. Indumentum
on underside of leaves, on branchlets and flower parts very densely
tomentose to floccose, hairs long and often individually visible.
Inflorescences terminal spicate or thyrsoid cymes, almost cylindrical.
Corolla purple, tube 5-6 mm long, 2-3 mm wide, stamens inserted at
||Leaves and branchlets tomentose (but less so than in (28a) B.
nivea, tomentulose or glabrescent.
||Leaf blade narrowly ovate to elliptic. Inflorescence spicate,
long-conical in shape, many flowered and showy. Corolla white, lilac,
blue or purple. Corolla tube 8-13 mm long, less than 2mm in diameter.
Flowering from mid-summer.
||Leaf blade elliptic or ovate. Inflorescence paniculate or thyrsoid
cyme, corolla white, pink or lavender. Flowering in the early spring.
||Both surfaces of leaf and petiole densely tomentose. Branchlets
terete, stellate tomentose, exterior of corolla tube tomentose,
stamens inserted in upper third.
||All parts less densely tomentose than in (20a) B. fallowiana.
Upper surface of leaf blade sub-glabrous, branchlets four-angled.
Exterior of corolla tube pubescent, not conspicuously tomentose,
stamens inserted at middle or towards the base.
||Leaf blade elliptic or narrowly so, up to 16cm in length,
acuminate at apex, margin entire, upper surface glabrous, fine
off-white to tan indumentum below. Inflorescence paniculate, lax,
axillary or terminal; corolla rose-pink or lavender, tube 11-16mm
long, 1.5-2 mm diameter, exterior sparsely to densely tomentose,
interior with few glandular hairs, stamens inserted slightly above
middle of the tube.
||Underside of leaves, petioles, branchlets and inflorescences
densely stellate-tomentose, but never floccose as in (28a) B. nivea.
Leaf blade narrowly ovate or elliptic, up to 25cm in length.
Inflorescence thyrsoid or paniculate.
||Leaf blade elliptic to ovate, upper surface glabrescent, underside
densely tomentose. Corolla white, pale lavender or lilac-pink,
corolla tube 8-10 mm long and 1.6-2.2 mm diameter Stamens inserted
approximately at one third of the tube length from the mouth of the
||Leaf blade narrowly ovate or elliptic, margin sometimes lobed,
upper surface slightly bullate and stellate tomentulose, lower surface
densely tomentose. Corolla white, pink or lavender, corolla tube 6-10
mm long, 1.2-1.6 mm diameter. Stamens inserted towards the mouth of
the corolla tube.