An Illustrated Flora of the Northern United States, Canada and the British Possessions/General Key to the Orders and Families

by Nathaniel Lord Britton & Addison Brown

General Key to the Orders and Families

Subkingdom Pteridophyta.

Spores developing into flat or irregular prothallia, which bear the reproductive organs (antheridia and archegonia); flowers and seeds none.
1.	Spores produced in sporanges, which are borne on the back of a leaf, in spikes or panicles, or in special conceptacles.	Order 1. Filicales.
	Spores all of one sort and size (isosporous families).
	Vernation erect or inclined; sporanges in spikes, or panicles, opening by a transverse slit.	Fam. 1. Ophioglossaceae.
	Vernation coiled; sporanges reticulated, usually provided with a ring (annulus).
	Sporanges opening vertically.
	Sporanges panicled, with a rudimentary ring; marsh ferns.	Fam. 2. Osmundaceae.
	Sporanges sessile on a filiform receptacle; leaves filmy, translucent.	Fam. 3. Hymenophyllaceae.
	Sporanges ovoid, in panicles, or spikes, provided with an apical ring.	Fam. 4. Schizaeaceae.
	Sporanges opening transversely, provided with a vertical ring; borne in sori on the back or margin of a leaf.	Fam. 5. Polypodiaceae.
	Spores of two sizes (microspores and macrospores).
	Plants rooting in the mud; leaves 4-foliolate, or filiform.	Fam.6. Marsileaceae.
	Plants floating; leaves entire, or 2-lobed.	Fam.7. Salviniaceae.
2.	Spores produced in sporanges, which are clustered underneath the scales of a terminal cone-like spike; stems jointed, rush-like.	Order 2. Equisetales.
	One family.	Fam. 8. Equisetaceae.
3.	Spores produced in sporanges, which are borne in the axils of scale-like or tubular leaves.	Order 3. Lyciodiales.
	Spores all of one sort and size.	Fam.9. Lycopodiaceae.
	Spores of two sizes (microspores and macrospores).
	Leaves scale-like, 4-many-ranked, on branching stems.	Fam. 10. Selaginellaceae.
	Leaves tubular, clustered on a corm-like trunk; aquatic or mud plants.	Fam. 11. Isoetaceae.

Subkingdom Spermatophyta.

Microspores (pollen-grains) developing into a tubular prothallium (pollen-tube); macrospores (embryo-sac) developing a minute prothallium, and, together with it, remaining enclosed in the macrosporange (ovule) which ripens into a seed.

Class 1. Gymnospermae.

Fruit a cone, with several or numerous scales, sometimes berry-like by their cohesion.	Fam. 1. Pinaceae.
Fruit (in our genus) a fleshy integument nearly enclosing the seed.	Fam. 2. Taxaceae.

Class 2. Angiospermae.

Ovules enclosed in an ovary.

Subclass 1. Monocotyledones.

Embryo with 1 cotyledon; stem with no distinction into pith, wood and bark; leaves mostly parallel-veined.

1.	Carpels 1, or more, distinct (united, at least partially, in Family 6, Scheuchzeriaceae, where they are mostly united until maturity, and Family 8, Vallisneriaceae, aquatic herbs, with monoecious or dioecious flowers); parts of the flowers mostly unequal in number.
	Inflorescence various, not a true spadix.
	Flowers not in the axils of dry chaffy scales (glumes); our species aquatic or marsh plants.
	Endosperm mealy or fleshy; perianth of bristles or chaffy scales; flowers monoecious, spicate or capitate.	Order 1. Pandanales.
	Flowers spicate, the spikes terminal. Flowers capitate, the heads axillary to leaf-like bracts.	Fam. 1. Typhaceae. Fam. 2. Sparganiaceae.
	Endosperm none, or very little; perianth corolla-like, or herbaceous, or none.
	Perianth wanting, or rudimentary.	Order 2. Naiadales..
	Carpels distinct; stigmas disk-like or cup-like. Carpels united; stigmas slender. Flowers axillary; leaves spinose-dentate. Flowers on a spadix; leaves grass-like.	Fam. 3. Zannichelliaceae.   Fam. 4. Naiadaceae. Fam. 5. Zosteraceae.
	Perianth present, of 2 series of parts.
	Carpels distinct.	Order 3. Alismales.
	Petals similar to the sepals; anthers mostly elongated.	Fam. 6. Scheuchzeriaceae.
	Petals not similar to the sepals; anthers short.	Fam. 7. Alismaceae.
	Carpels united.	Order 4. Hydrochariales.
	Ovary 1-celled with parietal placentae.	Fam. 8. Vallisneriaceae.
	Ovary 6-9-celled.	Fam. 9. Hydrocharitaceae.
	Flowers in the axils of dry chaffy scales (glumes), arranged in spikes or spikelets.	Order 5. Graminales       (Glumiflorae).
	Fruit a caryopsis (grain); stems (culms) mostly hollow in our species.	Fam. 10. Gramineae.
	Fruit an achene; stems (culms) solid.	Fam. 11. Cyperaceae.
	(Order 6, Palmales, including only the family Palmaceae, Palms, and Order 7, Cyclanthales, including only the family Cyclanthaceae, are not represented in our territory.)
	Inflorescence a fleshy spadix, with or without a spathe; or plants minute, floating free, the flowers few or solitary on the margin or back of the thallus.	Order 8. Arales       (Spathiflorae).
	Large herbs, with normal foliage and well-developed spadix.	Fam. 12. Araceae.
	Minute floating thalloid plants.	Fam. 13. Lemnaceae.
2.	Carpels united into a compound ovary; parts of the usually complete flowers mostly in 3's or 6's.
	Seeds with endosperm.
	Flowers regular, or nearly so (corolla irregular in Commclina and Pontederia).
	Endosperm mealy; ovary superior.	Order 9. Xyridales       (Farinosae).
	a. Ovary 1-celled.
	Aquatic moss-like leafy herbs; flowers solitary.	Fam. 14. Mayacaceae.
	Erect rush-like herbs; flowers in terminal scaly heads or spikes.	Fam. 15. Xyridaceae.
	Mud or aquatic herbs, the flowers subtended by spathes	(Heteranthera in Pontederiaceae).
	b. Ovary 2-3-celled (except in some Pontederiaceae).
	Flowers very small, densely capitate, monoecious or dioecious.	Fam. 16. Eriocaulaceae.
	Flowers perfect.
	Epiphytes; leaves scurfy.	Fam. 17. Bromeliaceae.
	Terrestrial or aquatic herbs; leaves not scurfy.
	Perianth of 2 series of parts, the outer (sepals) green, the inner (petals) colored.	Fam. 18. Commelinaceae.
	Perianth 6-parted.	Fam. 19. Pontederiaceae.
	Endosperm fleshy or horny; ovary superior or inferior.	Order 10. Liliales.
	a. Ovary superior (except in Aletris, in the Liliaceae, and some species of Zygadenus in the Melanthaceae).
	Perianth-segments distinct, green or brown, not petal-like; herbs with grass-like leaves and small flowers.	Fam. 20. Juncaceae.
	Perianth-segments distinct, or partly united, at least the inner petal-like.
	Fruit a capsule (except in Yucca baccata, where it is 'large, fleshy and indehiscent).
	Capsule mostly septicidal; plants rarely bulbous.	Fam. 21. Melanthaceae.
	Capsule loculicidal (septicidal in Calochortus); plants mostly bulbous.	Fam. 22. Liliaceae.
	Fruit a fleshy berry (except in Uvularia of the Convallariaceae).
	Erect herbs; tendrils none; flowers perfect.
	Leaves basal or alternate.	Fam. 23. Convallariaceae.
	Leaves verticillate.	Fam. 24. Trilliaceae.
	Vines, climbing by tendrils, or rarely erect ; flowers dioecious, in axillary umbels.	Fam. 25. Smilaceae.
	b. Ovary inferior, wholly or in part.
	Stamens 3, opposite the inner corolla-segments.	Fam. 26. Haemodoraceae.
	Stamens 6 in our species.
	Erect perennial herbs ; flowers perfect.	Fam. 27. Amaryllidaceae.
	Twining vines; flowers dioecious.	Fam. 28. Dioscoraceae..
	Stamens 3, opposite the outer corolla-segments.	Fam. 29. Iridaceae.
	Flowers very irregular; ovary inferior.	Order 11. Scitaminales.
	One family represented in our territory.	Fam. 30. Marantaceae.
	Seeds without endosperm, very numerous and minute; ovary inferior.	Order. 12. Orchidales       (Microspermae).
	Flowers regular; stem-leaves reduced to scales.	Fam. 31. Burmanniaceae.
	Flowers very irregular.	Fam. 32. Orchidaceae.

Subclass 2. Dicotyledones.

Embryo normally with 2 cotyledones; stems mostly differentiated into pith, wood and bark; leaves mostly net-veined.

Series 1. Choripetalae.

Petals distinct to the base, or wanting (exceptions noted)

---

A.

Petals none, except in Portulacaceae and in most Caryophyllaceae, which are herbs with leaves nearly always opposite, the seeds with endosperm, and in the pistillate flowers of the walnuts (Juglans).

1.

Calyx none (except in the Juglandaceae, which are trees with odd-pinnate leaves).

Marsh herbs with perfect flowers in nodding spikes.	Order 1. Piperales.
One family only.	Fam. 1. Saururaceae.
Trees or shrubs; staminate flowers, and sometimes also the pistillate, in aments.
Leaves odd-pinnate; fruit a nut enclosed in a husk.	Order 2. Juglandales..
One family only.	Fam. 2. Juglandaceae.
Leaves simple.
Fruit 1-seeded.	Order 3. Myricales.
Ovule erect, orthotropous.	Fam. 3. Myricaceae.
Ovule laterally attached, ascending, amphitropous.	Fam. 4. Leitneriaceae.
Fruit many-seeded; seeds with a tuft of hairs at one end.	Order 4. Salicales.
One family only.	Fam. 5. Salicaceae.

2.

Calyx present.

Flowers, at least the staminate ones, in aments.	Order 5. Fagales.
Both staminate and pistillate flowers in aments.	Fam. 6. Betulaceae.
Pistillate flowers subtended by an involucre, which becomes a bur or a cup in fruit.	Fam. 7. Fagaceae.
Flowers not in aments (in ament-like spikes in Morus), but variously clustered, rarely solitary.
a. Flowers monoecious, dioecious or polygamous (sometimes perfect in Ulmus); ovary superior, 1-celled.	Order 6. Urticales.
Fruit not an achene; trees, shrubs or herbs; ovule pendulous.
Trees with alternate leaves, the sap not milky. Trees with alternate leaves and milky sap.	Fam. 8. Ulmaceae. Fam. 9. Moraceae.
Fruit an achene; herbs with small clustered greenish flowers.
Ovule pendulous; styles or stigmas 2. Ovule erect or ascending; style or stigma 1.	Fam. 10. Cannabinaceae. Fam. 11. Urticaceae.
(Order 7, Proteales, extensively developed in the southern hemisphere, is not represented in our area.)

---

Series 2. Gamopetalae.

Petals more of less united. (See exceptions)

A. Ovary superior (except in Vacciniaceae and Symplocaceae, in which it is partly or wholly inferior).

Ι.

Stamens mostly free from the corolla, or adnate merely to its base (at the sinuses of the corolla in Diapensia and Pyxidanthera of the Diapensiaceae), as many as the lobes and alternate with them, or twice as many.

Order 1. Ericales.

• Stamens free from the corolla, or merely adnate to its base, not united into a tube.

• Ovary superior; fruit a capsule, or rarely drupaceous.

• Corolla essentially polypetalous.

• Ovary 3-celled; shrubs; leaves deciduous.
• Ovary 4-5-celled; low, mostly evergreen perennials.

Fam. 1. Clethraceae.

Fam. 2. Pyrolaceae.

• Corolla distinctly gamopetalous (except in Monotropa and Hypopitys of the Monotropaceae and Ledum of the Ericaceae).

• Herbaceous saprophytes without green leaves.
• Shrubs with normal, often evergreen leaves.

Fam. 3. Monotropaceae.

Fam. 4. Ericaceae.

• Ovary inferior, adnate to the calyx, forming a many-seeded berry in fruit.

Fam. 5. Vacciniaceae.

• Stamens borne at the sinuses of the corolla, or united in a 10-lobed tube.

Fam. 6. Diapensiaceae.

ΙI.

Stamens borne on the corolla, as many as its lobes and opposite them, or twice as many, or more.

• Herbs.

• Style 1; fruit a capsule.
• Styles 5; fruit an achene or utricle.

Order 2. Primulales.

Fam. 7. Primulaceae.

Fam. 8. Plumbaginaceae.

• Shrubs or trees.

• Stamens as many as the corolla-lobes.

• Stamens twice as many as the corolla-lobes. or more.

• Styles 2-8; flowers mostly monoecious or dioecious.
• Style 1, simple or lobed; flowers mostly perfect.

• Stamens in several series.
• Stamens in i series.

Order 3. Ebenales.

Fam. 9. Sapotaceae.

 

Fam. 10. Ebenaceae.

 

Fam. 11. Symplocaceae.

Fam. 12. Styracaceae.

III.

Stamens borne on the corolla, as many as its lobes or fewer, and alternate with them (in our species of Fraxinus and Forestiera of the Oleaceae there is no corolla).

• Corolla not scarious, nerved.

• Ovaries 2, distinct (except in some Loganiaceae, and in Gentianaceae and Menyanthaceae, in which the ovary is compound, with 2 cavities, or rarely more, or with 1 cavity and 2 placentae); flowers regular; stamens mostly adnate to only the lower part of the corolla; leaves mostly opposite.

Order 4. Gentianales
      (Contortae).

a.	Stamens (usually 2), fewer than the corolla-lobes, or corolla none; our species trees or shrubs.

Fam. 13. Oleaceae.

b.	Stamens as many as the corolla-lobes; mostly herbs.

• Stigmas distinct; juice not milky; ovary 1, compound.

• Ovary 2-celled; leaves stipulate, or their bases connected by a stipular line.

Fam. 14. Loganiaceae.

• Ovary 1-celled; celled; leaves not stipulate.

• Leaves opposite or rarely verticillate; corolla-lobes convolute or imbricated in the bud.

Fam. 15. Gentianaceae.

• Leaves basal or alternate ; corolla-lobes induplicate-valvate in the bud; marsh or aquatic herbs.

Fam. 16. Menyanthaceae.

• Stigmas united; juice milky; ovaries 2 in our species.

• Styles united; stamens distinct; pollen of simple grains.

Fam. 17. Apocynaceae.

• Styles distinct; stamens mostly monadelphous; pollen-grains united into waxy masses.

Fam. 18. Asclepiadaceae.

• Ovary 1, compound (2-divided in Dichondra; in Boraginaceae and Labiatae mostly deeply 4-lobed around the style) flowers regular or irregular; stamens mostly adnate to the middle of the corolla-tube or beyond; leaves opposite or alternate.

Order 5. Polemoniales
      (Tubiflorae).

a. Corolla regular (irregular in Echium of the Boraginaceae).

• Ovary not 4-lobed, the carpels not separating as separate nutlets at maturity.

• Ovary 2-divided.

Fam. 19. Dichondraceae.

• Ovary 2-celled, rarely 3-4-celled; style 1, entire, 2-cleft, or 2-parted; mostly twining vines.

• Leaves normal.

Fam. 20. Colvolvulaceae.

• White or yellowish parasitic vines, the leaves reduced to minute scales.

Fam. 21. Cuscutaceae.

• Ovary 3-celled; stigmas 3, linear; herbs, not twining.

Fam. 22. Polemoniaceae.

• Ovary 1-celled (2-celled in Nama) ; style 1, 2-lobed, or 2-parted; herbs, not twining.

Fam. 23. Hydrophyllaceae.

• Ovary deeply 4-lobed around the style, or not lobed (Heliotropium); carpels separating as nutlets.

Fam. 24. Boraginaceae.

b.	Corolla irregular, more or less 2-lipped (regular in Solanaceae, in Mentha and Lycopus of the Labiatae, and nearly or quite so in Verbena and Callicarpa of the Verbenaceae).

1. Carpels 1-2-seeded.

• Ovary not lobed, 2-4-celled, the style apical; carpels separating into 1-seeded nutlets.

Fam. 25. Verbenaceae.

• Ovary 4-lobed around the style, the lobes ripening into 1-seeded nutlets.

Fam. 26. Labiatae.

2. Carpels several-many-seeded (2-seeded in some Acanthaceae).

• Fruit a berry, or more commonly 1 capsule which is 1-2-celled, 2-valved, circumscissile, or irregularly bursting, not elastically dehiscent.

• Placentae axile.

• Ovary 2-celled, or rarely 3~5-celled.

• Flowers regular; fertile stamens 5 (4 in Petunia); fruit a berry or capsule.

Fam. 27. Solanaceae.

• Flowers more or less irregular; fertile stamens 2 or 4 (5 in Verbascum); fruit a capsule.

Fam. 28. Scrophulariaceae.

• Ovary 1-celled; marsh or aquatic herbs with flowers on scapes.

Fam. 29. Lentibulariaceae.

• Placentae parietal.

• Herbs, parasitic on the roots of other plants, the leaves reduced to scales, not green; ovary 1-celled.

Fam. 30. Orobanchaceae.

• Trees, vines, shrubs, or herbs, the foliage normal.

• Trees, shrubs, or woody vines; capsule 2-celled; seeds winged in our genera.

Fam. 31. Bignoniaceae.

• Opposite-leaved herbs; capsule 1-celled in our genus; seeds wingless.

Fam. 32. Martyniaceae.

• Capsule completely 2-celled, elastically loculicidally dehiscent; opposite-leaved herbs; placentae axile.

Fam. 33. Acanthaceae.

3.	Ovary and fruit 1-celled with 1 erect orthotropous ovule and seed; herb with spicate flowers and reflexed fruits.

Fam. 34. Phrymaceae.

• Corolla scarious, nerveless.

Order 6. Plantaginales.

• Herbs with small spicate or capitate flowers ; one family.

Fam. 35. Plantaginaceae.

B. Ovary inferior.
Ι.	Anthers distinct.
	Stamens as many as the corolla-lobes and alternate with them (one fewer in Linnaea of the Caprifoliaceae), or twice as many; ovary compound, with 1 ovule or more in each cavity; leaves opposite, or verticillate.	Order 7. Rubiales.
	Stamens as many as the corolla-lobes.
	Leaves always stipulate, usually blackening in drying.	Fam. 36. Rubiaceae.
	Leaves usually exstipulate, not blackening in drying.	Fam. 37. Caprifoliaceae.
	Stamens twice as many as the corolla-lobes; low herb with ternately divided leaves.	Fam. 38. Adoxaceae.
	Stamens mostly fewer than the corolla-lobes; ovary 1-celled with 1 pendulous ovule, or 3-celled with 2 of the cavities without ovules.	Order 8. Valerienales      (Aggregatae).
	Ovary 3-celled, 2 of its cavities empty. Ovary 1-celled; flowers densely capitate, involucrate.	Fam. 39. Valerianaceae. Fam. 40. Dipsacaceae.
ΙI.	Anthers united (except in Campanula and Specularia of the Campanulaceae, in Ambrosiaceae, and in Kuhnia of the compositae).	Order 9. Campanulales       (Campanulatae)
	Flowers not in involucrate heads; juice mostly milky.
	Endosperm none; flowers monoecious or dioecious; our species vines.	Fam. 41. Cucurbit aceae.
	Endosperm present, fleshy; flowers perfect.
	Flowers regular. Flowers irregular.	Fam. 42. Campanulaceae. Fam. 43. Lobeliaceae.
	Flowers in involucrate heads.
	Flowers all expanded into rays (ligulate); juice milky.	Fam. 44. Cichoriaceae.
	Flowers all tubular, or the outer expanded into rays; juice very rarely milky.
	Stamens distinct, or nearly so.	Fam. 45. Ambrosiaceae.
	Stamens united by their anthers into a tube around the style (except in Kuhnia).	Fam. 46. Compositae.