Centaurea sect. Acrocentron (Cassini, 1826) Candolle, 1838

Negaresh, Kazem, Yousefi, Zohreh & Kaya, Yusuf, 2023, A new species of Centaurea sect. Acrocentron (Asteraceae, Cardueae) from Iran, Phytotaxa 597 (1), pp. 37-50 : 44

Key to species of Centaurea sect. Acrocentron in Iran

1. Flowers yellow or whitish ..................................................................................................................................................................2

- Flowers purple or dark purple ............................................................................................................................................................3

2. Stems branched from lower to upper parts, with several capitula; involucres subglobose, 20–30 mm wide; appendages straw-coloured, 5–7 mm wide at base (cilia excluded); terminal spine 20–35 mm long; flowers yellow............................... C. sosnovskyi

- Stems simple, monocephalous; involucres cupuliform, 35–40 mm wide; appendages brown, 3–5 mm wide at base (cilia excluded); terminal spine 4–13 mm long; flowers whitish ............................................................................................................ C. zangulensis

3. Flowers dark purple................................................................................................................................................. C. kandavanensis

- Flowers purple ....................................................................................................................................................................................4

4. Plant entirely glabrous; appendages without spine .................................................................................................. C. sanandajensis

- Plant hairy; appendages with distinct spine........................................................................................................................................5

5. Involucres 12–18(–20) mm wide; appendages concealing minor part of phyllaries..........................................................................6

- Involucres (20–) 25–35 mm wide; appendages concealing totally or major part of phyllaries ..........................................................9

6. Plants dwarf, up to 5 cm height; basal and lower cauline leaves lyrate; spine <12 mm long...........................................................7

- Plants tall, (20–) 30–60 cm height; basal and lower cauline leaves pinnatisect or pinnatipartite; spine> 12 mm long.....................8

7. Stems densely floccose-tomentose; leaves above loosely floccose-tomentose, below sparsely pilose-articulate; involucres 12–13 mm wide; phyllaries glabrous; appendages brown, 1–2.5 mm wide at base (cilia excluded); achenes 3.8–4 mm long; pappus 6–6.2 mm long...................................................................................................................................................................... C. bojnordensis

- Stems densely arachnoid; leaves loosely arachnoid; involucres (12–) 15–20 mm wide; phyllaries loosely arachnoid; appendages straw-coloured or light brown, 2–4 mm wide at base (cilia excluded); achenes 4.2–4.8 mm long; pappus 8–9 mm long ................. ........................................................................................................................................................................................ C. serowensis

8. Plants perennial, many-stemmed; stems branched from basal to upper parts; involucres 15–18 mm wide; appendages 3–5 mm wide at base (cilia excluded); pappus (8–) 10–11 mm long.......................................................................................................... C. irritans

- Plants biennial, few-stemmed; stems branched only in upper part; involucres 18–22 mm wide; appendages 1–3 mm wide at base (cilia excluded); pappus 5–6 mm long ................................................................................................ C. carduiformis subsp. iranica

9. Stems floccose-tomentose or arachnoid-tomentose .........................................................................................................................10

- Stems pilose or hirsute-articulate .....................................................................................................................................................11

10. Basal and lower cauline leaves pinnatisect or pinnatipartite; involucres 30–35 mm long; appendages dark brown or blackish, 3–4 mm wide at base (cilia excluded); terminal spine 8–18(–22) mm long; achenes 5–5.2 mm long; pappus 6.5–7 mm long ................ .................................................................................................................................................................................... C. orumiehensis

- Basal and lower cauline leaves lyrate; involucres (30–)35–40(–45) mm long; appendages straw-coloured or pale brown, 6–9 mm wide at base (cilia excluded); terminal spine 20–30(–40) mm long; achenes 6–7 mm long; pappus (8–) 9–14 mm long................... .............................................................................................................................................................. C. urvillei subsp. deinacantha

11. Pappus 13–15 mm long .................................................................................................................................................. C. luristanica

- Pappus 6–9(–11) mm long................................................................................................................................................................12

12. Appendages straw-coloured .............................................................................................................................................................13

- Appendages brown or dark brown ...................................................................................................................................................14

13. Involucres (20–) 25–30 mm wide; appendages (5–) 6–7 mm wide at base (cilia excluded); terminal spine 21–30(–35) mm long; cilia (10–)12–15 on each side, 6–9 mm long .................................................................................................................... C. ochrocephala

- Involucres 16–23 mm wide; appendages 4–5 mm wide at base (cilia excluded); terminal spine 10–20(–27) mm long; cilia 8–10 on each side, (3–)4–5(–6) mm long.......................................................................................................................................... C. persica

14. Basal leaves 30–42 cm long; appendages brown or light brown, 1.5–2.5 mm wide at base (cilia excluded); cilia 5–8 on each side; achenes ca. 5 long........................................................................................................................................................ C. khosraviana

- Basal leaves 10–20 cm long; appendages dark brown, blackish or brown, 4–8 mm wide at base (cilia excluded); cilia (8–)10–13 on each side; achenes 5.5–6 long .....................................................................................................................................................15

15. Stems usually branched from lower to upper parts; terminal spine of median appendages 20–30 mm long .............. C. sintenisiana

- Stems branched in median or upper parts; terminal spine of median appendages (5–)10–15(–20) mm long .................................16

16. Plants biennial; basal and lower cauline leaves pinnatisect, with up to 10 lateral segments; involucres 30–35 × 30–35 mm; appendages 5–8 mm wide at base (cilia excluded); pappus 10–11 mm long............................................................ C. elegantissima

- Plants perennial; basal and lower cauline leaves lyrate, with 2–4 lateral segments; involucres 20–25 × (15–)18–22(–25) mm; appendages 3–5 mm wide at base (cilia excluded); pappus 6–9 mm long ( C. pseudoscabiosa ) .....................................................17

17. Terminal spine of appendages 10–15(–20) mm long ..................................................................... C. pseudoscabiosa subsp. armata

- Terminal spine of appendages (2–)3–6(–8) mm long.......................................................................................................................18

18. Involucres narrower, 14–17 mm wide; appendages small, ca. 2 mm wide at base (excluding cilia); cilia 1.5–2(–2.5) mm long....... .................................................................................................................................................... C. pseudoscabiosa subsp. araratica

- Involucres broader, 20–30 mm wide; appendages medium-sized, 3–4 mm wide at base (excluding cilia); cilia (2–) 3–5 mm long .. ..........................................................................................................................................................................................................19

19. Plant 40–90 cm tall; stems branched in upper part........................................................... C. pseudoscabiosa subsp. pseudoscabiosa

- Plant up to 35 cm tall; stems simple or branched from near base .................................................. C. pseudoscabiosa subsp. glehnii