Asteraceae (tribe Heliantheae) subtribe Helianthinae
(synonym of Asteraceae tribe Heliantheae subtribe Helianthinae)
Tithonia
sunflowerweed, tithonia
erect, branched.
usually mostly cauline, rarely mostly basal; mostly opposite (distal often alternate) or mostly alternate, rarely whorled;
petiolate or sessile;
blades (often 3- or 5-nerved) orbiculate or deltate to lanceolate or linear (and intermediate shapes), sometimes lobed, ultimate margins entire or toothed, faces usually hairy (often hispid to scabrellous), often gland-dotted.
all or mostly cauline; opposite (proximal) or mostly alternate;
petiolate or sessile;
blades often (1-), 3-, or 5-nerved, mostly deltate or pentagonal [lanceolate, linear], sometimes 3- or 5-lobed, bases ± truncate or auriculate [attenuate] (sometimes decurrent onto petioles), ultimate margins serrate to crenate, faces glabrate, ± hirsute, pilose, soft-pubescent, or villous, often gland-dotted.
cylindric to hemispheric or rotate.
campanulate to hemispheric, 10–20+ mm diam.
usually flat or convex, sometimes hemispheric or conic, usually paleate (epaleate in Lagascea; paleae usually falling, sometimes persistent, mostly oblong to linear, often conduplicate, herbaceous to scarious, apices sometimes ± 3-lobed or -toothed; becoming hardened perigynia completely investing cypselae in Sclerocarpus).
hemispheric to convex, paleate (paleae persistent, embracing cypselae, striate, ± 3-toothed, middle teeth larger, stiff, acute or acuminate to aristate).
0 or 5–30(–100+), neuter, or styliferous and sterile;
corollas usually yellow to orange, sometimes partly or wholly brown to purple or red-brown to reddish.
8–30, neuter;
corollas yellow or orange.
1 (Lagascea) or 10–200(–1000+), bisexual, fertile;
corollas usually yellow to orange, sometimes brown to purple or reddish to red-brown, tubes shorter than or about equaling cylindric or funnelform throats, lobes 5, ± deltate (equal);
anther thecae dark or pale;
stigmatic papillae usually continuous.
40–120[–200+], bisexual, fertile;
corollas yellow, tubes shorter than throats (bases of throats bulbous and hairy), lobes 5, ± triangular (anthers black, brown, or tan, bases cordate-sagittate, appendages ovate; style branches relatively slender, appendages penicillate or lanceolate to attenuate).
persistent, 4–45(–100+) in 1–6+ series (usually distinct, ± connate in Lagascea, broadly ovate to linear, subequal or unequal).
persistent, 12–28+ in 2–5 series (linear to broadly rounded, unequal to subequal, apices acute to rounded).
0.
usually radiate, sometimes discoid, borne singly or in corymbiform (paniculiform or racemiform) arrays (glomerules or second-order heads of 1–2-flowered heads in Lagascea).
borne singly (peduncles usually distally dilated, fistulose).
often ± compressed, flattened, biconvex, clavate, columnar, obovoid, obpyramidal, or prismatic (lengths usually 1–2 times diams.), glabrous or hairy (faces and/or angles);
pappi 0, or (often readily falling or fragile, sometimes persistent) usually of (1–)2(–8+) (sometimes aristate) scales and/or awns, sometimes coroniform.
(black or brown) ± compressed or flattened, often 3- or 4-angled or biconvex, ± cuneiform in silhouette (sometimes with basal elaiosomes);
pappi 0, or ± coroniform (of ± connate scales, 1–2 scales sometimes subulate to aristate).
= 17.
Asteraceae (tribe Heliantheae) subtribe Helianthinae
Tithonia
Genera 17, species 363 (8 genera, 69 species, including 1 hybrid, in the flora).
Circumscription of Helianthinae adopted here (i.e., that of H. Robinson 1981) is narrower than traditional circumscriptions (e.g., T. F. Stuessy 1977[1978]), which included genera here treated in Ecliptinae, Galinsoginae, and Rudbeckiinae.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species 11 (3 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Phyllaries 4–5 in ± 1 series (connate); disc florets 1(–2; the 1–2-flowered heads aggregated in glomerules or second-order heads) | Lagascea |
1. Phyllaries 5–45(–100+) in (1–)2–6+ series (distinct); disc florets (10–)15–200(–1000+) | → 2 |
2. Receptacles paleate (each palea completely investing and falling with a cypsela, eachforming a hardened perigynium) | Sclerocarpus |
2. Receptacles paleate (paleae sometimes conduplicate, ± enfolding cypselae, not forming perigynia) | → 3 |
3. Heads borne singly (peduncles usually distally dilated, fistulose) | Tithonia |
3. Heads borne singly or in corymbiform, paniculiform, racemiform, or thyrsiform arrays (peduncles rarely, if ever, notably dilated or fistulose) | → 4 |
4. Cypselae flattened, thin-margined | Simsia |
4. Cypselae ± compressed, biconvex, or 3- or 4-angled, often obpyramidal | → 5 |
5. Cypselae glabrous or glabrate; pappi 0 | → 6 |
5. Cypselae usually ± strigose, sometimes glabrous or glabrate; pappi of 2–6+, persistent, readily falling, or tardily falling scales | → 8 |
6. Shrubs (leaves often lobed, lobes usually 3–9, ± linear) | Viguiera |
6. Annuals or perennials (leaves not lobed) | → 7 |
7. Annuals; leaf blades lanceolate to linear; involucres 5–6 mm diam.;phyllaries 11–17 | Helianthus |
7. Annuals or perennials; leaf blades lance-linear, lanceolate, ovate, rhombic, or rhombic-ovate; involucres 6–14 mm diam.; phyllaries14–25 | Heliomeris |
8. Shrubs; involucres 5–9 mm diam | Bahiopsis |
8. Annuals or perennials; involucres (5–)7–40+ mm diam | → 9 |
9. Pappi readily falling | Helianthus |
9. Pappi persistent or tardily falling | Viguiera |
1. Perennials, subshrubs, or shrubs; phyllaries 16–28; ray laminae 48–69 mm; disc florets 80–120+; cypselae 4–6 mm | T. diversifolia |
1. Annuals; phyllaries 12–16; ray laminae 9–15 or 20–33 mm; disc florets 40–60 or 60–90; cypselae 5–9 mm | → 2 |
2. Leaf blades ± deltate to pentagonal, often 3- or 5-lobed, abaxial faces soft-pubescent; rays usually orange, rarely yellow, laminae 20–33 × 6–17 mm | T. rotundifolia |
2. Leaf blades mostly deltate, rarely, if ever, lobed, abaxial faces sparsely hirsute (hairs larger on veins); rays yellow, laminae 9–15 × 4–6 mm | T. thurberi |
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