Clerodendrum, Linnaeus (1753: 637)

Meerts, Pierre, 2023, The genus Clerodendrum (Lamiaceae) in the flora of Central Africa (D. R. Congo, Rwanda, Burundi), Phytotaxa 594 (1), pp. 1-42 : 2-5

CLERODENDRUM Linnaeus (1753: 637)

Type:— Clerodendrum infortunatum Linnaeus (1753: 637) .

Trees, shrubs, lianas, or more rarely perennial herbs; stem quadrangular. Leaves opposite or 3–4-whorled, usually petiolate, simple; lamina entire, undulate, repand, dentate or crenate; petiole articulated, sometimes the lower part persisting as a woody spine. Inflorescence of axillary cymes, generally grouped in racemose or corymbose thyrses; bracts often foliaceous, bracteoles small, mostly not exceeding calyx. Flower: calyx usually regular, campanulate to tubular or cup-shaped, ± deeply 5-lobed or truncate, sometimes 5-angled, usually persistent and accrescent in fruit; corolla symmetrical in bud or, if asymmetrical, usually expanding abruptly on upper side due to resupination, actinomorphic; tube ± long, narrowly cylindrical or funnel-shaped; limb of 5 equal or subequal spreading or reflexed lobes, larger than the others. Stamens 4, inserted on the corolla tube, usually long exserted; anthers versatile. Carpels 2, each incompletely divided into 2 loculi; locules 1-ovulate. Style terminal, stigma exserted, 2-fid, the lobes equal, short. Fruit drupaceous, obovoid or globose, generally 4-lobed, often appearing 1-lobed by abortion; endocarp separated into four 1-seeded pyrenes.

References:— Baker (1900); Briquet (1895); Fernandes (1998, 2005); Harley et al. (2004); Huber (1963); Lebrun & Stork (1997); Li et al. (2016); Moldenke (1985a); Pollard (2022); Robyns (1947); Thomas (1936); Malaise (1985); Verdcourt (1992).

Note:—Two species have been collected in cultivation in only one occasion and are not dealt with in the following account: Clerodendrum trichotomum Thunberg (1784: 256) (D.R. CONGO. Eala, 5 April 1932, Corbisier-Baland 1361 (BR!)); Clerodendrum chinense ( Osbeck 1757: 215) Mabberley (1989: 707) (D.R. CONGO. Kinshasa, Gombe, 27 August 2001, Pauwels 8540 (BR!)).

The species present in our territory belong in the following sections of the genus, as defined by Thomas (1936), validated and amended by Verdcourt (1992).

Sect. Capitata Verdc.

C. buchneri , C. capitatum , C. excavatum , C. frutectorum , C. poggei .

Sect. Eurycalyx Thomas ex Verdc.

C. bipindense , C. melanocrater , C. thyrsoideum , C. volubile .

Sect. Macrocalyx Thomas ex Verdc.

C. baumii , C. buettneri , C. fuscum , C. pynaertii , C. rotundifolium C. thomsoniae , C. welwitschii .

Sect. Microcalyx Thomas ex Verdc.

C. formicarum , C. inaequipetiolatum , C. johnstonii , C. polycephalum .

Sect. Oxycalyx Thomas ex Verdc.

C. buchananii , C. splendens , C. umbellatum .

Sect. Siphonocalyx Thomas ex Verdc.

C. dewittei , C. fasciculatum , C. schweinfurthii , C. silvanum , C. tanganyikense .

All the species in this account belong in the African clade except C. buchananii , an introduced species which belongs in the Asian clade as defined by Steane et al. (1997).

Key to the species of Clerodendrum in Central Africa (D. R. Congo, Rwanda, Burundi)

1. Corolla wholly orange to red.................................................................................................................................................. Group 1

- Corolla white, cream, yellowish, greenish, occasionally red-spotted in throat or with one red lobe.................................................2

2. Inflorescence congested, capitate, with axis hidden by flowers; calyx membranous, petaloid, whitish, yellowish, purplish or mauve, 10–26 mm long....................................................................................................................................................................... Group 2

- Inflorescence looser, branched, or relatively compact but, in this case, calyx greenish, not petaloid, 3–10(–12) mm long .............3

3. Inflorescence congested, hemispheric to globose, with branches inconspicuous at anthesis ................................................ Group 3

- Inflorescence of loose cymes, or elongate thyrses, with branches conspicuous at anthesis ..............................................................4

4. Calyx lobes at anthesis 0.5–3 mm long, <50(–60)% of total calyx length............................................................................ Group 4

- Calyx lobes at anthesis (3–) 5–25 mm long,> 50% of total calyx length............................................................................... Group 5

Group 1: Corolla wholly orange or red

1. Calyx whitish to yellowish, pentagonal, gibbose at base, 12–25 mm long........................................................................................2

- Calyx greenish or reddish, neither pentagonal nor gibbose, 3–10 mm long ......................................................................................3

2. Stem and inflorescence branches densely pubescent, with brown hairs; leaves conspicuously pubescent ..... Clerodendrum fuscum

- Stem and inflorescence branches subglabrous or puberulous; leaves glabrous ........................................ Clerodendrum thomsoniae

3. Petiole 2–25 cm; lamina deeply cordate at base; lower surface of lamina tomentose .............................. Clerodendrum buchananii

- Petiole 0.3–2(–4) cm; lamina rounded to slightly cordate at base; lower surface of lamina glabrous or shortly pubescent on veins (rarely on whole surface).............................................................................................................................. Clerodendrum splendens

Group 2: Inflorescence capitate, unbranched; calyx petaloid> 10 mm

1. Inflorescences on old defoliated shoots often near ground level; leaves glabrous..................................... Clerodendrum excavatum

- Inflorescences on leafy twigs; leaves pubescent at least on lower surface ........................................................................................2

2. Suffrutex (0.10–) 0.15–1 m in height, with shoots renewed every year; corolla tube 5–7.5 cm; leaf lamina <11 × 5.5 cm ............... ....................................................................................................................................................................... Clerodendrum buchneri

- Shrub or liana 1–6 m, with persisting shoots; corolla tube 6–19 cm; lamina of variable size, often> 11 × 5.5 cm ..........................3

3. Shrub with unbranched or sparingly branched shoots; petiole base not persistent; leaves mostly grouped at shoot apex; lamina 9–48 × 6–45 cm, mostly cordate at base; petiole mostly> 6 cm ................................................................................................................4

- Shrub or liana with branched shoots; petiole base persistent, spiny; leaves not grouped near shoot tip; lamina <17 × 11 cm, cuneate or rounded at base; petiole <6 cm ............................................................................................................... Clerodendrum capitatum

4. Inflorescence ovoid to subcylindric, 5–20 cm long (corolla excluded), markedly longer than wide; peduncle hollow, up to 10 mm thick; stem and petiole papillate, lacking long patent hairs; calyx purplish-violaceous ................................... Clerodendrum poggei

- Inflorescence hemispheric to shortly ovoid, 3–5 cm in diam. (corolla excluded); peduncle not exceeding 5 mm in diam., mostly solid; stem and petiole with mixed indumentum of papilliform and long patent hairs; calyx mostly greenish, occasionally with a purplish tinge ............................................................................................................................................. Clerodendrum frutectorum

Group 3: Inflorescence congested, hemispheric; calyx green at anthesis, <10 mm long

1. Calyx 3–5 mm long; peduncle papillate, pubescent, or tomentose ....................................................................................................2

- Calyx 5–9 mm long; peduncle glabrous to puberulous......................................................................................................................3

2. Corolla tube 25–35 mm long; petiole and young twigs glabrous or with patent stiff hairs; peduncle 4–22 cm, papillate, puberulous or shortly pubescent............................................................................................................................... Clerodendrum schweinfurthii

- Corolla tube 15–20 mm long; petiole and young twigs beige to fulvous tomentose; peduncle 1.5–4 cm, densely pubescent to tomentose................................................................................................................................................. Clerodendrum fasciculatum

3. Calyx narrowly tubular, 2–4 mm wide near throat, lobes not conspicuously veined; corolla tube 7--13(--18) mm long; stamens exserted 5--10(--15) mm; petiole glabrous; liana up to 10 m ................................................. Clerodendrum silvanum f. caulanthum

- Calyx funnel-shaped, ca. 5 mm wide near throat, lobes conspicuously 3-veined; corolla tube 15–22 mm long; stamens exserted 10–15 mm; petiole pubescent; suffrutex or small liana <2 m in height ......................................................... Clerodendrum dewittei

Group 4: Inflorescence conspicuously branched; calyx lobes 0.5–3 mm long, <50(–60)% of total calyx length

1. Calyx shortly campanulate to cupular, with depth equal to or smaller than diameter; calyx lobes spreading...................................2

- Calyx tubular to narrowly funnel-shaped, with depth markedly longer than diameter; calyx lobes erect.........................................5

2. Inflorescence on old defoliated shoots, often near the ground................................................................... Clerodendrum bipindense

- Inflorescence on leafy shoots .............................................................................................................................................................3

3. Whole plant turning black in herbarium; corolla dark-spotted after anthesis (in the field); lamina base rounded to obtusely cuneate ................................................................................................................................................... Clerodendrum melanocrater

- Whole plant green to brownish in herbarium; corolla not dark-spotted after anthesis; lamina base cuneate ....................................4

4. Flower bud and corolla tube greyish-tomentellous; inflorescence main axis pubescent; inflorescence paniculiform; rachis 6–40 cm, with internodes 5–65 mm ......................................................................................................................... Clerodendrum thyrsoideum

- Flower bud and corolla tube subglabrous; main axis of inflorescence subglabrous or puberulent only in the upper part; inflorescence corymbiform; rachis 1.5–6(–12) cm, with internodes <10 mm ...................................................................... Clerodendrum volubile

5. Leaves 3–4-whorled; lamina conspicuously 3-veined from base, glabrous; inflorescence umbelliform, rachis 1–2(–7) cm, inflorescence branches almost horizontally spreading, glabrous to puberulous; stem often conspicuously striate or sulcate ............ ................................................................................................................................................................... Clerodendrum formicarum

- Leaves opposite, or, more rarely, 3-whorled, but, in this case, pubescent; lamina 1-nerved at base; inflorescence thyrsiform or, rarely, umbellate; stem cylindric or slightly striate ............................................................................................................................6

6. Calyx (3–) 4–10 mm long, lobed ca. ¼ in length; corolla tube 7–20 mm ..........................................................................................7

- Calyx 2.5–6 mm, lobed 40–50% in length; corolla tube 4–10(–11) mm ...........................................................................................8

7. Stem (at least near apex) and leaves (at least the petiole), more or less pubescent; upper surface of lamina dull, with reticulum not prominulent............................................................................................................................................ Clerodendrum tanganyikense

- Stem and leaves wholly glabrous; upper surface of lamina shiny, with reticulum prominulent................... Clerodendrum silvanum

8. Calyx glabrous to puberulent; first-order inflorescence axes branched only near tip, spreading at a very open angle, forming an umbel; leaves often 3-whorled .............................................................................................................. Clerodendrum polycephalum

- Calyx pubescent, either hirsute or with dense indumentum of curly hairs; first order inflorescence axes more ramified, forming a corymbose to hemispheric inflorescence; leaves opposite.................................................................................................................9

9. Young twigs, inflorescence branches and calyx covered with short curly rusty or fulvous hairs; inflorescence 4–14 × 4–19 cm; petiole 1–9 cm; lower surface of lamina most often tomentose, with curly hairs, sometimes only on veins ...................................... ..................................................................................................................................................................... Clerodendrum johnstonii

- Young twigs, inflorescence branches and calyx with straight or undulate, not curly, pale fulvous hairs; inflorescence 3–4 × 3.5–8 cm; petiole <5.5 cm; lamina hispid on lower surface of veins...................................................... Clerodendrum inaequipetiolatum

Group 5: Inflorescence branched; calyx divided over ca. 50% of its length, with lobes> (3–) 5 mm

1. Liana or shrub; shoots perennial, branched,> 1 m long ....................................................................................................................2

- Suffrutex; shoots annual, unbranched, up to 1.2 m long ....................................................................................................................7

2. Inflorescence terminal, rather dense, with branches <2.5(–4) cm, not subtended by leafy bracts........... Clerodendrum welwitschii

- Inflorescence in axillary cymes subtended by foliaceous bracts, branches> 3 cm, occasionally the uppermost ones grouped into a loose corymb or panicle......................................................................................................................................................................3

3. Shoot and inflorescence with long patent, brownish-violaceous articulated hairs 2–5 mm long ................. Clerodendrum buettneri

- Shoot and inflorescence glabrous or shortly pubescent, with hairs not remarkable ..........................................................................4

4. Corolla tube 6–11 cm long; calyx densely velvety-pubescent; leaf lamina tomentose on lower surface; pedicel 1--4 cm; stem hollow..................................................................................................................................................... Clerodendrum rotundifolium

- Corolla tube 1–3 cm; calyx glabrous to shortly pubescent; leaf lamina glabrous or slightly pubescent on lower surface; pedicel 0.4–1.8(–3.0) cm; stem solid ..............................................................................................................................................................5

5. Calyx cream to yellow; stem and inflorescence branches densely pubescent, with brown hairs; inflorescence branches subtended by foliaceous, subsessile, cordate, clasping bracts ........................................................................................... Clerodendrum fuscum

- Calyx whitish to whitish-green, occasionally purple-tinged; stem and inflorescence axes puberulous to shortly pubescent; inflorescence branches subtended by ovate, petiolate, not clasping, foliaceous bracts .....................................................................6

6. Inflorescence comprised of small 3–5(10)-flowered axillary cymes on a peduncle 0.6–3 cm, in the 3–10 upper nodes of the stem, forming a very loose narrow thyrse (9–32 × 3–6 cm); calyx gibbose at base, pentagonal, accrescent to 20 mm during anthesis...... ....................................................................................................................................................................... Clerodendrum pynaertii

- Inflorescence comprised of multiflorous corymbiform cymes, peduncle 1–9 cm, in the 2–3 upper nodes; calyx funnel-shaped or campanulate, neither gibbose nor pentagonal, <12 mm long................................................................... Clerodendrum umbellatum

7. Calyx gibbose, truncate at base, 10–16 mm long at anthesis, accrescent up to 18–23 mm long; inflorescence branches 1–2 cm; corolla tube ca. 10 cm long............................................................................................................................... Clerodendrum baumii

- Calyx funnel-shaped, neither gibbose nor truncate, 6–12 mm long; inflorescence branches 1–9 cm; corolla tube ca. 1.5 cm long... ................................................................................................................................................................... Clerodendrum umbellatum