Hysterionica, Willdenow, 1807

Deble, Leonardo Paz, 2021, Hysterionica chamomilloides (Asteraceae: Astereae) a new species from the grassland ecosystem of Río de La Plata, Phytotaxa 482 (1), pp. 36-44 : 41-42

Key to South American species of Hysterionica

1. Leaves with margin entire (rarely the most basal leaves with margin few toothed) ..........................................................................2

- Leaves with margin irregularly incise-toothed, or deeply lobed .................................................................................................... 14

2. Annual herbs.......................................................................................................................................................................................3

- Perennial herbs or subshrubs ..............................................................................................................................................................4

3. Ray flowers 1–2-seriate, corolla white.............................................................................................................. Hysterionica resinosa

- Ray flowers 3–4-seriate, corolla yellow............................................................................................................... Hysterionica bakeri

4. Basal leaves in rosulate leaf arrangement, sometimes become dry at the end of the anthesis...........................................................5

- Leaves distributed uniformly along the stem .................................................................................................................................... 9

5. Pulvinate dwarf subshrubs. Ray flowers with white corolla. Cypselae fusiform or oblong-fusiform, not compressed or slightly compressed, 4–7-ribbed......................................................................................................................................................................6

- Perennial herbs. Ray flowers with yellow corolla. Cypselae compressed, with two lateral ribs .......................................................7

6. Leaves 15–60 × 1–3 mm, adaxial surface pubescent .................................................................................. Hysterionica dianthifolia

- Leaves 4–15 × 0.3–0.9 mm, adaxial surface glabrous .................................................................................... Hysterionica pulvinata

7. Leaf-blades sericeous-pubescent ..................................................................................................................... Hysterionica pulchella

- Leaf-blades sparsely pubescent, trichomes not applied to surface.....................................................................................................8

8. Pappus composed by 2-series of bristles ................................................................................... Hysterionica aberrans var. hunzikeri

- Pappus composed by a unique series of bristles........................................................................... Hysterionca aberras var. aberrans

9. Leaves often lanceolate or elliptic in shape, 1.5–6 mm wide. Cypselae 2–4-ribbed .......................................................................10

- Leaves often filiform or linear in shape, 0.4–2 mm wide. Cypselae 4–10-ribbed ...........................................................................12

10. Plants seemingly glabrous. Leaves grayish-green, rigid in texture............................................................... Hysterionica glaucifolia

- Plants with abundant filiform trichomes. Leaves thin in texture......................................................................................................11

11. Leaves covered by hispid trichomes, 1.5–4 mm long. Outer pappus composed by filiform bristles, 1.5–2 mm long ........................ ...................................................................................................................................................................... Hysterionica jasionoides

- Leaves covered by strigose trichomes, thickened at base, 0.3–1 mm long. Outer pappus composed by scales, 0.4–0.8 mm long .... .......................................................................................................................................................................... Hysterionica cabrerae

12. Ray flowers with white corolla. Outer pappus composed by a crown of scales, 0.5–1 mm long. Cypselae obovate, slightly compressed, 4–5-ribbed, 0.8–1.4 mm long ........................................................................................... Hysterionica chamomilloides

- Ray flowers with yellow corolla. Outer pappus composed by few bristles. Cypselae obovate-fusiform, 7–10-ribbed, 1.4–2.8 mm long...................................................................................................................................................................................................13

13. Ray flowers 3–4-seriate. Leaves with abundant hispid trichomes; blades linear-filiform, at base truncate, 0.6–1 mm wide ............. ......................................................................................................................................................................... Hysterionica filiformis

- Ray flowers 1–2-seriate. Leaves with absent or scarce trichomes; blades linear-oblong or linear-lanceolate, at base semiamplexicaul, 1–2 mm wide............................................................................................................................... Hysterionica pinifolia

14. Leaves with margin irregularly incised-toothed. Outer pappus composed by few scales (ca. 2–4) .................................................... ................................................................................................................................................................ Hysterionica matzenbacheri

- Leaves with margin deeply lobed. Outer pappus composed by a crown of scales (ca. 6–8) ...........................................................15

15. Leaves densely hairy, segments slightly acute, obtuse or rounded ..................................................................................................16

- Leaves glabrous or with scarce sericeous trichomes, segments acute or acuminate.................................. Hysterionica pinnatisecta

16. Leaves with segments linear-oblong, 5–10 × 0.8–1.5 mm. Ray flowers 12–15 mm long, much exceeding the involucre................. ......................................................................................................................................................................... Hysterionica nebularis

- Leaves with segments obovate or elliptic, 5–15 × 2–5 mm, Ray flowers 6–8 mm long, slightly exceeding the involucre ................ ...................................................................................................................................................................... Hysterionica pinnatiloba