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marigold

Habit Annuals, perennials, subshrubs, or shrubs [perennials], mostly 10–80(–200) cm.
Stems

erect, branched distally or ± throughout.

Leaves

cauline; mostly opposite (distal sometimes alternate);

petiolate or sessile;

blades mostly lanceolate to oblanceolate overall, usually 1–3-pinnately lobed or -pinnatisect, ultimate margins toothed or entire, faces glabrous or hairy (oil-glands scattered and/or submarginal).

Involucres

narrowly cylindric or fusiform to turbinate or broadly campanulate, 1–12+ mm diam.

Receptacles

convex to conic, smooth or finely pitted, epaleate.

Ray florets

0 or 1–8(–13+) (to 100+ in “double” cultivars), pistillate, fertile (except “double” cultivars);

corollas yellow or orange, red-brown (with or without yellow/orange), or white.

Disc florets

6–120+, bisexual, fertile;

corollas greenish yellow to orange, sometimes tipped with red or red-brown, tubes much longer than or about equaling funnelform throats, lobes 5, deltate to lance-linear (equal or 2 sinuses deeper than others).

Phyllaries

persistent, 3–21+ in 1–2 series (connate to 7/8+ their lengths, usually streaked and/or dotted with oil-glands).

Calyculi

0.

Heads

radiate or discoid, borne singly or in ± corymbiform arrays.

Cypselae

narrowly obpyramidal or fusiform-terete, sometimes weakly flattened, glabrous or hairy;

pappi persistent, of 2–5(–10) dissimilar, distinct or connate scales in ± 1 series: 0–5+ oblong to lanceolate, erose-truncate or laciniate plus 0–2(–5) longer, subulate to aristate.

x

= 12.

Tagetes

Distribution
from USDA
Tropical and warm-temperate America; especially Mexico [Introduced in Old World]
[BONAP county map]
Discussion

Species 40+ (4 in the flora).

Some Tagetes species (e.g., T. erecta) produce nematicidal thiophenes in their roots and have been shown to be effective controls for nematodes in diverse crops (cf., http://www.ncagr.com/agronomi/nnote1.htm).

Reports of “Tagetes minima L.” for Pennsylvania (cf. http://plants.usda.gov) are evidently rooted in an error for T. minuta. Report of T. pusilla Kunth (= T. filifolia Lagasca) for Maryland (http://plants.usda.gov) was not verified for this treatment.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key
1. Leaf lobes (or simple blades) linear to filiform, 10–25(–35+) × 0.5–1.5 mm
T. micrantha
1. Leaf lobes lance-elliptic or lanceolate to lance-linear, 12–25(–50+) × (2–)4–8(–12+) mm
→ 2
2. Perennials, subshrubs, or shrubs
T. lemmonii
2. Annuals
→ 3
3. Heads in ± corymbiform clusters; peduncles 1–5+ mm; involucres 7–10+ × 1.5–3 mm
T. minuta
3. Heads borne ± singly; peduncles 30–100(–150+) mm; involucres 10–22 × (3–)5–12+ mm
T. erecta
Source FNA vol. 21, p. 235. Author: John L. Strother.
Parent taxa Asteraceae > tribe Heliantheae > subtribe Pectidinae
Subordinate taxa
T. erecta, T. lemmonii, T. micrantha, T. minuta
Name authority Linnaeus: Sp. Pl. 2: 887. (1753): Gen. Pl. ed. 5, 378. (1754)
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