What’s a dichotomous key?
Help
Hieracium
See list of 17 species in this genusSell (1987) argued convincingly, on morphological grounds, for the segregation of Pilosella from Hieracium. Gaskin and Wilson (2007) showed that Pilosella is a monophyletic group. However, they also showed that recognition of Pilosella creates a paraphyletic Hieracium unless the genus Stenotheca, a genus of western hemisphere plants, is also recognized. The morphological distinction between Hieracium and Stenotheca is relatively weak and does not seem to justify generic separation. Therefore, the genus Hieracium is recognized here in the broad sense until such time as study elucidates morphological separation of Stenotheca from Hieracium. References: Voss (1996), Strother (2006c).
-
1a. Cypsela body 1.2–2 (–2.2) mm long, each rib on the surface of the ovary projecting to form a crenulate apex [Fig. 422]; pappus bristles mostly 25–40 in 1 series [Fig. 422]; rays yellow, yellow with an red abaxial stripe, or orange-red; stems scapose, without leaves or with few and reduced leaves; leaves tapering to an ill-defined petiole; plants with a well-developed rosette of basal leaves at anthesis, commonly with stolons [Fig. 426]
-
2a. Reproductive stems bearing a solitary capitulum or a capitulescence with 2–4 (–6) capitula on elongate peduncles (5–) 15–150 mm long [Fig. 426]; leaf blades 2–4 (–6) times as long as wide; plants 3–25 (–40) cm tall
-
3a. Capitulescence with 1 or 2 (–3) capitula [Fig. 426]; involucres 7.5–9 (–10) mm tall; leaf blades densely pubescent with stellate hairs on the abaxial surface, the hairs usually contiguous and concealing the surface
-
3b. Capitulescence with (1–) 2–4 (–6) capitula; involucres (9–) 10–13 mm tall; leaf blades moderately pubescent with stellate hairs on the abaxial surface, the hairs not so numerous as to be contiguous
-
-
2b. Reproductive stems bearing (3–) 5–30 (–50) capitula, these usually in compact, corymb-like capitulescences on short peduncles 1–15 (–28) mm long; leaf blades 3–8 times as long as wide; plants (10–) 20–100 cm tall
-
4a. Ray flowers orange-red (drying dark red); involucral bracts 1.5–3 mm wide
-
4b. Ray flowers yellow; involucral bracts 0.5–1.25 mm wide
-
5a. Involucres 7.5–9 mm tall; pappus bristles 4–5 (–6) mm long; ray corollas 8–12 mm long; leaf blades green, with abundant setae adaxially; plants with short or, more commonly, long rhizomes and often also short, prostrate stolons
-
5b. Involucres 5–6 (–7) mm tall; pappus bristles 3–4 mm long; ray corollas 6–9 mm long; leaf blades glaucous, sparsely and unevenly setose to subglabrous adaxially; plants usually with short, praemorse rhizomes and also usually lacking prostrate stolons (sometimes with divergent to ascending branches)
-
6a. Peduncles lacking stellate hairs or with very few stellate hairs; basal leaf blades lacking stellate-hairs on the abaxial surface, either glabrous or with simple, eglandular hairs; involucral bracts mostly 0.5–0.75 mm wide
-
6b. Peduncles moderately to densely pubescent with stellate hairs; basal leaf blades sometimes with minute stellate-hairs on the abaxial surface (longer, simple, eglandular ones may be present as well); involucral bracts mostly 0.75–1 mm wide
-
-
-
-
-
1b. Cypsela body (2–) 2.5–5 mm long, each rib apically confluent to form an obscure ring [Fig. 424]; pappus bristles mostly 30–60 (or more) in 2 series; rays yellow; stems scapose or evidently leafy; lower leaves usually tapering to a ± distinct petiole; plants with a basal rosette of leaves or these withered at anthesis, never with stolons
-
7a. Reproductive stems with (4–) 6–50 leaves; basal leaves mostly absent or withered at anthesis, not forming a conspicuous rosette
-
8a. Involucres 6–7 mm tall; pappus bristles 4–5 mm long; ray corollas 5–8 mm long; capitula with 8–20 (–30) flowers; peduncles very slender, 0.2–0.3 mm thick
-
8b. Involucres 7–10 (–11) mm tall; pappus bristles (4.5–) 5–7 mm long; ray corollas 8–18 mm long;
-
9a. Cypsela body tapering to an expanded, circular apex where the pappus bristles attach [Fig. 423]; capitula with 20–40 flowers; capitulescence panicle-like, cylindrical in outline, with short lower branches
-
9b. Cypsela body truncate or scarcely narrowed to the circular apex [Fig. 424]; capitula with (30–) 40–100 flowers; capitulescence corymb-like or umbel-like, with elongate lower branches (sometimes narrow and panicle-like in H. scabrum)
-
10a. Peduncles with abundant stipitate glands [Fig. 427]; leaf blades entire or remotely denticulate
-
10b. Peduncles with very few or no stipitate glands; at least the lower leaf blades usually dentate
-
11a. Hairs of the lower stem and leaf surfaces simple, firm, and bulbous-based, short compound hairs usually absent from the leaf surfaces
-
11b. Hairs of the lower stem and leaf surfaces simple or compound, but not bulbous-based, that of the leaves sometimes compound
-
12a. Involucral bracts tapering to an acuminate apex; reproductive stems 10–35 cm tall, with 4–10 leaves (in part)
-
12b. Involucral bracts tapering to a narrow-rounded to acute apex; reproductive stems 15–60 (–150) cm tall, with 6–50 leaves
-
13a. Leaf blades linear to lanceolate or narrow-oblong, the principal ones 3–15 (–19) mm wide, mostly 4–12 times as long as wide, provided with abundant stout, rigid, conical hairs, at least toward the margin of the blade
-
13b. Leaf blades lanceolate to oblong-lanceolate or narrow-ovate, the principal ones (7–) 12–40 mm wide, mostly 2–5 times as long as wide, lacking rigid, conical hairs or these very sparse
-
-
-
-
-
-
-
7b. Reproductive stems with 0–5 (–10) leaves, these often reduced and bract-like; basal leaves present at anthesis, forming a conspicuous rosette
-
14a. Leaf blades entire or merely denticulate, adaxially green to glaucous-green and usually with red to purple coloration that closely follows the outline of the veins; ray corollas 7–11 mm long; mid-portion of reproductive stem glabrous or nearly so
-
14b. At least the lower leaf blades with conspicuous, sharp teeth, adaxially green, red coloration, when present, either more randomly patterned (i.e., mottled) or merely suffusing a region of the blade; ray corollas 12–18 mm long; mid-portion of reproductive stem with setose or glandular hairs or both
-
15a. Basal leaf blades truncate to cordate at the base; reproductive stems with 0–2 leaves
-
15b. Basal leaf blades tapering to the base; reproductive stems with 2–10 leaves
-
16a. Leaf blades 7–20 mm wide; peduncles lacking stipitate glands; plants 10–35 cm tall (in part)
-
16b. Leaf blades 15–50 mm wide; peduncles stipitate-glandular; plants 30–60 (–100) cm tall
-
17a. Leaf blades with red to red-purple blotches, streaks, and/or spots [Fig. 425]; stem leaves mostly numbering 2–4; involucres with numerous stipitate glands
-
17b. Leaf blades green, without red to red-purple coloration; stem leaves numbering mostly 2–8; involucres with few to numerous stipitate glands
-
-
-
-
-
Show photos of:
Each photo represents one species in this genus.