Croton undetermined

Beyer, J., Esser, H. - J., Eurlings, M. C. M. & Welzen, P. C. van, 2023, A revision of the genus Croton (Euphorbiaceae) in Sumatra (Indonesia), Blumea 68 (1), pp. 1-25 : 7

KEY TO CROTON SPECIES OF SUMATRA

1. Annual herbs, up to 0.4 m high............10. C. hirtus

1. Climbers, shrubs or trees, with distinctly woody stem, higher than 0.4 m .................................... 2

2. Young and mature leaves completely and densely pubescent abaxially, appearing silvery-whitish to golden or brownish, epidermis not visible (not even with a hand lens)...... 3

2. Mature leaves with dense to scattered trichomes abaxially or glabrous, not completely silvery-whitish or golden-brown, epidermis visible............................... 5

3. Indumentum consisting of only lepidote trichomes, with 60–80 fused radii. Higher order leaf nerves very indistinct. Capsules distinctly 3-lobed, obovoid, deeply sulcate................................... 4. C. cascarilloides

3. Indumentum consisting of stellate to lepidote trichomes, with less than 40 fused radii or radii free. Higher order leaf nerves distinct. Capsules globose, not to hardly sulcate. 4

4. Leaves (2–)2.4–3.5 times longer than wide, the very base rounded to subcordate. Basal leaf glands (0.1–) 0.5–0.9 mm diam. Staminate flowers 4–5 mm diam. Pistillate flowers 4.5–6 mm diam. Capsules 5–7 mm high 1. C. adumbratus

4. Leaves 1.5–2.3(–2.9) times longer than wide, the very base distinctly cordate and slightly peltate. Basal leaf glands 1–1.5 mm diam. Staminate flowers 5–6.5 mm diam. Pistillate flowers 8–9 mm diam. Capsules (10–) 13–19 mm high.................................... 2. C. argyratus

5. Leaves basally slightly to distinctly triplinerved, secondary veins 3–7 pairs................................ 6

5. Leaves basally not or very indistinctly triplinerved, secondary veins (4–)6–17 pairs............................ 8

6. Leaf blade narrowly elliptic, 2.5–7.2 by 0.7–2.2 cm. Inflorescences to 2.5 cm long............. 16. C. viridifolius

6. Leaf blade elliptic, more than 2.5 cm wide. Inflorescences longer than 2.5 cm .............................. 7

7. Plant a straggling shrub, woody climber or liana, distinctly pubescent. Leaf blade with marginal glands. Capsules with thick woody pericarp................. 5. C. caudatus 7. Plant a non-climbing shrub or tree, soon glabrescent. Leaf blade without marginal leaf glands. Capsules with thin fragile pericarp....................... 15. C. tiglium

8. Leaf margin (sub)serrate to crenate, never entire, teeth either topped with a patch of simple trichomes or distinct marginal glands (colleters) present................ 9

8. Leaf margin entire to shallowly serrate (rarely distinctly serrate), teeth never topped with a patch of simple trichomes; marginal glands (colleters) absent............... 10

9. Leaf blade obovate (to elliptic), 2.5–10(–12) by 1.2–4.1 cm. Capsules c. 5 mm high, c. 5 mm diam......................................... 9. C. heterocarpus

9. Leaf blade elliptic, 15–30(–35) by 5–10 cm. Capsules c. 28 mm high, c. 22 mm diam.... 12. C. macrocarpus

10. Leaf glands abaxially on midrib base or leaf base. Abaxial leaf side with scattered but distinct trichomes to densely pubescent.................................. 11

10. Leaf glands abaxially on the very apex of the petiole. Abaxial leaf side (sub)glabrous.................. 14

11. Leaf glands lateral on the abaxial base of the midrib. 12

11. Leaf glands abaxially at the very base of the leaf, close to but not on the midrib.......................... 13

12. Stellate trichomes on leaves 0.4–0.9 mm diam,with (11–)15– 25(–30) free radii. Leaf blade narrowly elliptic, (3.1–)3.4– 5.2 times longer than wide, abaxial side slightly to densely pubescent. Inflorescences shorter than 5.5 cm. Capsules globose, slightly sulcate............ 7. C. gageianus

12. Stellate trichomes on leaves 0.1–0.4(–0.6) mm diam, with 11–17 free radii. Leaf blade elliptic, (1.9–)2.3–3.3(–3.8) times longer than wide, abaxial side with scattered trichomes to densely pubescent. Inflorescences longer than 6 cm. Capsules distinctly 3-lobed, obovoid, extremely sulcate............................. 8. C. griffithii

13. Leaf glands slightly to distinctly stalked discs, (0.4–) 0.6–1 mm diam, stalk 0.1–0.3 mm long. Leaf blade elliptic to obovate, 5.5–18 by 2.7–7.5 cm, 1.7–2.8 times longer than wide; secondary veins 8–10 pairs. Inflorescences (7–) 10–20 cm long. — Simalur/Simeulue Island.................................... 14. C. simalurensis

13. Leaf glands slightly stalked discs, 0.2–0.4 mm diam, stalk 0.1–0.2 mm long. Leaf blade narrowly elliptic, 2.5–7.2 by 0.7–2.2 cm, 2.4–4.2 times longer than wide; secondary veins 4–6 pairs. Inflorescences 0.5–2.5 cm long. — Sumatera Barat (West Sumatra) Province 16. C. viridifolius

14. Indumentum on leaves consisting of only lepidote trichomes, flat, with 20–40 completely fused radii.. 13. C. scalaeus

14. Indumentum on leaves consisting of only stellate trichomes, flat to slightly porrect, often with a central short porrect radius, with 8–20(–30) free to basally slightly fused trichomes.................................... 15

15. Leaf glands sessile ( Fig. 2a or 2e), flat, 0.8–1.5 mm diam................................. 6. C. coriifolius

15. Leaf glands stalked or sessile but elevated ( Fig. 2c or 2d), 0.1–0.6(–1) mm diam, stalk 0.1–0.5(–1) mm high... 16

16. Stipules filiform to subulate, 0.3–0.5 mm wide. Inflorescences 2–7 cm long. Sepals (both pistillate and staminate) with scattered trichomes to densely pubescent on outside. Capsules globose, 4–5 by 4–5 mm, rough, hardly sulcate, very densely pubescent.............. 3. C. beccarii

16. Stipules subulate, 0.5–1 mm wide. Inflorescences 5–23 cm long. Sepals (both pistillate and staminate) glabrous to subglabrous on outside. Capsules distinctly 3-lobed, obovoid, 5–8(–13) by 4–7 mm, smooth, sulcate, with scattered trichomes........................ 11. C. laevifolius

Figures

Fig. 2 Different types of leaf glands. a. Croton heterocarpus, glands sessile and placed more adaxially on the apex of the petiole; b. C. caudatus, glands 1–3 pairs, distinctly stalked and abaxially on the midrib base; c. C. viridifolius, glands slightly stalked and located either on the leaf blade base or as in drawing on the side veins; d. C. macrocarpus: glands with a thick stalk located on the midrib base; e. C. adumbratus: glands sessile on the midrib base (a: LÖrzing 13830; b: Forbes 2989; c:Kleinhoonte 460; d:de Wilde & de Wilde­Duyfjes 20590; e:de Wilde & de Wilde­Duyfjes 19604; all L). — Illustration by Esmée Winkel,2021.