This is one of the easiest of all families to recognize, but one of the most difficult as far as identification of species is concerned. The flowers are small and 5-merous, except that the sepals are tiny or even absent and the carpels are 2. The inferior ovary ripens into a unique schizocarp in which 2 indehiscent, 1-seeded mericarps typically separate from a forking central axis that bears a mericarp suspended from the tip of each fork. Each mericarp usually has 5 longitudinal ribs, which may be relatively inconspicuous, or raised, or expanded into distinct wings. The flowers are in a head or simple umbel in a few genera (Eryngium, Sanicula), but in the great majority of our genera the inflorescence is a compound umbel, the primary branches, termed rays, each bearing an umbellet of pediceled flowers, some of which in some species may be staminate rather than bisexual. There may be bracts (an involucre) at the base of the primary umbel, and/or there may be bractlets (an involucel) at the base of each umbellet.
Vegetatively, the Apiaceae are ordinarily characterized by hollow internodes, petioles with expanded ± sheathing bases, and resin canals, which are readily sensed in the aromatic foliage and often seen as prominent oil tubes on the fruit. Many pungent and fragrant species are used in flavoring foods and medicines, while others provide familiar vegetables, and most of these escape from cultivation at least occasionally. Other species are deadly poisonous if taken internally. The leaves of Apiaceae are usually compound to deeply dissected and are often difficult to describe, especially since they may vary from the base to the summit of the stem. Ordinarily, the best results with the key will be obtained by using leaves from the middle of the stem (unless others are specified).
Since plants of most species have umbels of mixed ages, partly if not fully mature fruit is often available along with flowers. Measurements of the styles, unless stated to the contrary, include the expanded style base or stylopodium, and refer to the length that the style quickly attains by the time the petals are all shed. (Styles at anthesis may be minute, but on even the young fruit elongate.) Measurements of fruit do not include any persistent style or stylopodium. The fruit is sometimes flattened “dorsally” (parallel to the adjoining faces of the mericarps) and sometimes “laterally” (at a right angle to the adjoining faces).
A number of species cause severe dermatitis in sensitive people, especially Angelica sp., Pastinaca sativa, and most strongly Heracleum mantegazzianum.
1. Margins of cauline leaves and bracts of the inflorescence with stiff spines; basal leaves simple, unlobed; cauline leaves simple (at most 3–7-lobed), on stiff erect stem; flowers in a dense bracted head.
1. Margins of leaves and bracts without spines (or soft spines in Sanicula); basal leaves deeply lobed to compound or dissected, or if simple, the cauline leaves either compound or on a prostrate stem; flowers in umbels, at least some clearly pediceled.
2. Leaves all simple, with entire margins.
2. Leaves (at least the cauline) compound, dissected, or deeply lobed or toothed (basal or uppermost leaves sometimes simple).
3. Ovary and fruit pubescent, papillose, or bristly, or upper part of stem and peduncles with spreading or tomentose pubescence, or both conditions present.
4. Bristles of ovary and fruit all strongly hooked (with incurved tips); leaves once-palmately compound or deeply lobed; umbellets consisting of 1 or more sessile or subsessile bisexual flowers and pediceled staminate flowers, or entirely of staminate flowers.
4. Bristles or hairs (if any) of ovary and fruit only partly or weakly and slightly if at all curved at the tips; leaves various (mostly pinnate or deeply divided) but not once-palmately lobed; umbels in most species consisting of all bisexual flowers.
5. Cauline leaves (at least the upper ones) pinnately or bipinnately divided into long linear-lanceolate lobes, grading into simple, at most shallowly lobed, basal leaves.
Pimpinella (in part)
5. Cauline and basal leaves either both finely dissected or with definite leaflets mostly ca. 1 cm or more wide.
6. Leaves pinnate and with leaflets (or segments if dissected) less than 1 cm broad; introduced species, mostly in disturbed places.
7. Bracts (at least the larger ones) subtending the rays over (10–) 15 mm long (except sometimes when very young), pinnate with narrow lobes.
7. Bracts all less than 15 mm long, simple.
8. Leaves once-pinnately compound, the leaflets deeply lobed, with flat segments; ovaries and fruit with some bristles.
8. Leaves 2–3 times compound, with filiform segments; ovaries and fruit merely papillose-warty.
6. Leaves definitely ternate, with 3 principal (and petioluled) divisions at the summit of the petiole, and/or with ± clear-cut leaflets at least 1 cm broad.
9. Primary rays of umbel 1–7; fruits even when young, ± round in cross-section, lacking clear ribs or wings.
10. Ovary and fruit glabrous; plant a low, weak-stemmed annual.
Chaerophyllum (in part)
10. Ovary and fruit pubescent, the fruit with stiff appressed hairs especially toward the base; plant an erect perennial.
9. Primary rays of umbel at least 8; fruit variously shaped, strongly flattened, winged, or ribbed.
11. Fruit ca. 18–25 mm long; leaves finely dissected into ultimate segments less than 1 cm broad.
11. Fruit 1.6–12 (–14) mm long; leaves (at least the lower ones) with segments 1–12 cm broad.
12. Fruits ca. 1.6–2.5 mm long; upper stem leaves entire, with linear lobes.
Pimpinella (in part)
12. Fruits ca. 3–12 (–14) mm long; upper stem leaves toothed, ovate.
13. Leaflets mostly ca. 1–2 cm broad (rarely narrower), with regular obtuse teeth (occasionally lobed near the base); fruit less than 8 mm long, with conspicuous thin wings, the central part with ribs the entire length more prominent than the oil tubes.
13. Leaflets much more than 2 cm broad, with acute lobes and teeth; fruit ca. 8–12 (–14) mm long, not winged, with ribs less prominent than the dark oil tubes (which extend less than the full length).
Heracleum (in part)
3. Ovary and fruit smooth (except for ribs or wings) and glabrous, and upper part of stem glabrous (minutely pubescent in Pastinaca).
14. Principal cauline leaves (unless submersed) clearly once-pinnately compound with 5 or more definite flat leaflets (entire or toothed).
15. Flowers yellow; stem and leaves ± finely pubescent (very rarely glabrous); introduced, common weeds, often in dry places.
15. Flowers white; stem and leaves completely glabrous; native species, mostly in moist or wet places.
16. Leaflets entire or with a few irregularly spaced teeth (usually on apical half only); fruit ca. 4–5.5 mm long, strongly flattened dorsally.
16. Leaflets all toothed the full length of their margins; fruit ca. 1.5–3 mm long, rounded or flattened laterally.
17. Most (or all) cauline leaves with leaflets less than 3 (–4) times as long as broad, with teeth of very irregular size; fruit ca. 1.5–2 mm long, obscurely ribbed.
17. Most (or all) cauline leaves with leaflets (3.5–) 4–10 (–14) times as long as broad, with numerous fine teeth of ± uniform size; fruit ca. 2–3 mm long, with prominent corky ribs.
14. Principal cauline leaves trifoliolate, or palmate, or more than once-compound to deeply lobed, or finely divided into numerous flat to filiform toothed or entire segments.
18. Plant bearing vegetative bulblets, subtended by broad-based acuminate bracts, on upper parts.
18. Plant without bulblets.
19. Principal cauline leaves twice-pinnate (sometimes appearing ternate) with ± irregularly toothed ultimate segments ca. 3–10 mm broad; stem terete (or finely ridged), not grooved; umbellets subtended by narrow bractlets (scarcely if at all broader, at the base, than the rays); flowers yellow; fruit with corky marginal wing thicker than the body but with only obscure ribs on back; rare taprooted prairie species.
19. Principal cauline leaves more than twice-compound (sometimes clearly ternate) with ultimate segments various but if more than 3 mm broad and irregularly toothed, the stem grooved, the umbellets with broader bractlets, and/or the fruit with wing none or thin (though ribs may be prominent on back); species of various habit.
20. Cauline leaves (at least of middle and upper part of stem) finely divided, the ultimate lobes or segments ± filiform to linear-lanceolate and less than 5 mm wide.
21. Ultimate segments of at least the upper leaves slenderly linear-filiform, less than 1 mm wide and several times as long, and all entire; escapes from cultivation, at least the ripe fruit with spicy or aromatic quality.
22. Primary rays of umbel 3–7; styles ca. 1.5–2 mm long; fruit nearly spherical, hardly splitting into mericarps; petals very unequal in size, the larger ca. 3–4 mm long, white (to pink).
22. Primary rays of umbel (6–) 8–50; styles less than 1.2 mm long; fruit longer than broad, readily splitting; petals essentially uniform, not over 1.5 (–2) mm long, white or yellow.
23. Petals white; styles (excluding base) becoming at least 0.5 mm long; primary rays of umbel (6–) 8–14 (–16); rays and pedicels often subtended by 1 or more bracts.
23. Petals yellow (-green); styles (excluding base) less than 0.5 mm long; primary rays of umbel ca. (10–) 17–50; rays and pedicels without subtending bracts.
24. Petiolar sheaths ca. 1–2.5 cm long; mericarps bordered by a narrow wing at maturity; styles (including base) ca. 0.5 mm long on maturing fruit; annual.
24. Petiolar sheaths (at least the larger ones) ca. 3–9 cm long; mericarps without wing; styles (including relatively long base) ca. 1 mm long on maturing fruits; perennials.
21. Ultimate leaflets or segments of leaves (upper as well as lower) linear-oblong, mostly ca. 1–5 mm wide, less than 5 times as long as wide, sometimes toothed; escapes or native species, with rank or little “umbelliferous” odor but not spicy-aromatic.
25. Umbellets subtended by conspicuous bractlets much broader than the thickness of the rays.
26. Bractlets blunt or rounded at the tip, symmetrical beneath the umbellet; primary rays of umbel 1–4; leaves ternate above the sheathing petiole (divided into 3 ± equal axes); low native species blooming in the spring.
27. Fruit elongate (ca. 3.5–10 times as long as broad); anthers yellow; styles minute; plant usually lightly hairy (petioles, bractlets, stems, rays); annuals.
Chaerophyllum (in part)
27. Fruit no longer than broad; anthers deep maroon; styles elongate, exceeding the ovary and almost or quite as long as the fruit; plant glabrous; perennials from a ± spherical tuber.
26. Bractlets acute (cuspidate to acuminate or subulate) at the tip, all on one side of the umbellet; primary rays of umbel ca. (8–) 10–20; leaves pinnate (central axis more prominent than the lateral ones); tall erect introduced species (usually near habitation) blooming in the summer.
28. Stem strongly corrugated or angled, minutely pubescent toward base, unspotted; petiolar sheath densely pubescent at least at summit; fruit elongate, ca. 3 times as long as wide.
28. Stem nearly terete (slightly ridged), glabrous throughout, spotted with red-purple; petiolar sheath glabrous, fruit ovoid, less than twice as long as wide.
25. Umbellets with bractlets scarcely (toward base) if at all broader than the thickness of the primary rays.
29. Nodes pubescent with short stiff hairs; petals pale yellow; leaflets ± ovate-lanceolate and coarsely toothed or lobed.
Thaspium chapmanii (in part)
29. Nodes glabrous; petals white (yellow-green in Petroselinum); leaflets deeply divided into ± linear to lanceolate or oblong lobes.
30. Styles becoming 1.3–2 mm long; fruit strongly flattened dorsally, with 3 prominent ribs in the middle of each winged mericarp; tall native species of swampy and springy places.
30. Styles less than 1.3 mm long; fruit ± rounded or slightly flattened laterally, with 5 prominent ribs on each wingless mericarp; escapes from cultivation, in disturbed ground or near gardens.
31. Bractlets (or some of them) extending beyond the flowers; ribs on fruit broader than the intervals (nearly concealed) between them; leaves flat; pedicels and rays of umbel ± scabrous.
31. Bractlets subtending umbellets not extending beyond flowers; ribs on fruit much narrower than the intervals between them; leaves usually ± undulate; pedicels and rays of umbel smooth.
20. Cauline leaves with definite leaflets mostly over 1 cm broad, entire or (usually) toothed but not dissected into narrow lobes.
32. Cauline leaves with 3 leaflets (though these may be ± deeply lobed).
33. Petals yellow; fruit less than 7 mm long and less than twice as long as wide.
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33. Petals white; fruit over twice as long as broad or over 8 mm long.
34. Leaflets usually sessile or nearly so, glabrous; fruit less than 7 mm long, more than twice as long as broad; stem slender (less than 8 mm thick).
34. Leaflets all on distinct petiolules (terminal one longer), pubescent; fruit 8–12 mm long, less than twice as long as broad; stem stout, (8–) 10–30 mm thick or more.
Heracleum (in part)
32. Cauline leaves (except sometimes the uppermost) with more than 3 leaflets.
35. Leaflets entire or with ca. 1–5 coarse and irregular lobes or teeth (mostly beyond the middle); petals yellow.
36. Margins of all leaflets strictly entire; umbel and umbellets without bracts or bractlets, the rays and pedicels smooth; widespread native species in (usually) sandy soils.
36. Margins of most or all leaflets with a few teeth or small lobes; umbel and/or umbellets subtended by bracts, the rays and pedicels ± scabrous or papillose; rare native species or escapes from cultivation.
37. Nodes glabrous; fruit ribbed but not winged, with evident large style base; umbels and umbellets both subtended by well developed bracts and bractlets broader than the rays and pedicels respectively; escapes from cultivation, near habitations.
37. Nodes pubescent with very short stiff hairs; fruit strongly winged, without enlarged style base; umbels and umbellets with inconspicuous slender bracts or bractlets narrower than the rays and pedicels; very rare native species.
Thaspium chapmanii (in part)
35. Leaflets with numerous ± uniform and regularly spaced small teeth; petals yellow or white.
38. Plant with terete purple main stem ca. 8–40 mm (or more) in diameter; expanded petiolar sheaths ca. 1–6 cm broad at the middle and often (6–) 8–15 cm long; mature fruit ca. 6–8 mm long.
38. Plant with stem (mostly not purple) less than 8 (–15) mm in diameter (or larger in water); expanded petiolar sheaths narrower and shorter; mature fruit less than 6 (–7) mm long.
39. Petals yellow.
40. Leaflets ± minutely pubescent or hispidulous, at least beneath; fruit without raised ribs or wings on the broad side, ca. 5–6 (–7) mm long; style (including a large base) becoming ca. 1 mm or less long.
Pastinaca (in part, depauperate plants)
40. Leaflets glabrous (or ± scabrous-papillose only on main veins); fruit with elevated ribs or wings, ca. 3.5–4.5 mm long; style without a large base, slender throughout and becoming ca. 1–1.7 mm long.
41. Central flower of each umbellet staminate and pediceled; fruit pediceled, with several distinct thin wings on each side, evident even when half-mature.
Thaspium (in part)
41. Central flower (if bisexual) and fruit of each umbellet sessile or nearly so (if staminate, then pediceled); fruit with prominent ribs but not winged.
39. Petals white, or plants with only immature to mature fruit.
42. Leaflets with veins directed to sinuses between the teeth (with branch to tooth), or plant with vegetative bulblets on distal portion (or with both conditions); petals white.
Cicuta (in part)
42. Leaflets with veins directed to or into the teeth; plant without bulblets; petals white or yellow.
43. Style base becoming ca. 0.5 mm long; petals white.
43. Style base not at all developed; petals yellow.
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