This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
a. Flowers regular.
Pistils usually several or numerous (one only in Cercocarpus and some species of Alchemilla and Aphanes; in Sanguisorba, Poteridium and Poterium). Carpels distinct, sometimes adnate to the calyx, ripening into follicles or achenes.
Fam. 54. Rosaceae. 2: 242. Carpels united, enclosed by the calyx-tube and adnate to it, the fruit a pome.
Fam. 55. Malaceae. 2: 286. Pistil only 1.
Ovary 2-ovuled; fruit a drupe; leaves simple. Fam. 56. Amygdalaceae. 2: 322.
Ovary several-ovuled; fruit a legume; leaves 2-3-pinnate. Fam. 57. Mimosaceae. 2: 330.
b. Flowers irregular (nearly or quite regular in Gleditsia and Gymnocladus.
trees of the Caesalpiniaceae).
Fruit a legume; upper petal enclosed by the lateral ones in the bud; leaves compound, mostly stipulate. Fam. 58. Caesalpiniaceae. 2: 334.
Fruit spiny, indehiscent; leaves simple, exstipulate. Fam. 59. Krameriaceae. 2: 340.
Fruit a legume or loment; upper petal enclosing the lateral ones in the bud; leaves compound (sometimes i-foliolate), stipulate. Fam. 60. Fabaceae. 2:341.
4. Carpels united into a compound ovary; sepals mostly distinct.
* Stamens few, rarely more than twice as many as the sepals.
t Stamens as many as the sepals or fewer, and opposite them, or more numerous. t Ovules mostly pendulous, with the raphe toward the axis of the ovary.
Order 16. Geraniales. Stamens more than one; land plants.
Filaments partially united (distinct in some Geraniaceae); herbs, the leaves not punctate. Leaves not pinnately compound.
Capsule at length splitting into its 5 carpels; leaves lobed or dissected.
Fam. 61. Geraniaceae. 2:425. Capsule 2-5-celled, not splitting into its carpels.
Stamens 2-3 times as many as the petals; leaves 3-foliolate in our species.
Fam. 62. Oxalidaceae. 2: 430. Stamens as many as the petals; leaves entire. Fam. 63. Linaceae. 2: 435.
Leaves pinnately compound. Fam. 66. Zygophyllaceae. 2: 442.
Filaments distinct (united in some Balsaminaceae).
Flowers very irregular; calyx with a spurred or saccate sepal.
Fam. 64. Balsaminaceae. 2: 440. Flowers regular;
Herbaceous plants with pinnately divided leaves. Fam. 65. Limnanthaceae. 2:441.
Our species trees or shrubs with compound leaves, often punctate; flowers dioecious or polygamous. Leaves punctate. Fam. 67. Rutaceae. 2: 443.
Leaves not punctate, but the bitter bark with oil-sacs.
Fam. 68. Simaroubaceae. 2: 445. Flowers very irregular; petals 3; stamens usually 8; ours low herbs.
Fam. 69. Polygalaceae. 2: 446.
Flowers regular, often apetalous, small, monoecious or dioecious; carpels mostly 3; herbs or low shrubs, mostly with milky juice. Fam. 70. Euphorbiaceae. 2: 452.
Stamen only 1; perianth none; styles 2; small aquatic or rarely terrestrial plants with opposite entire leaves. Fam. 71. Callitrichaceae. 2: 477.
%% Ovules pendulous, with the raphe away from the axis of the ovary, or erect or ascending.
Order 17. Sapindales. Petals none (or 3 in Empetrum); flowers monoecious or dioecious; leaves evergreen.
Stamens mostly 3; low heath-like shrubs. Fam. 72. Empetraceae. 2: 478.
Stamens 4-7; our species an herb with broad leaves and spiked flowers.
Fam. 73. Buxaceae. 2: 480. Petals present; leaves deciduous, except in Cyrillaceae and some Ilicaceae.
Ovary i-celled (in ours); fruit a small drupe. Fam. 74. Anacardiaceae. 2: 480.
Leaves simple, pinnately veined. Seeds not arilled.
Fruit dry; flowers racemed, perfect. Fam. 75. Cyrillaceae. 2: 485.
Fruit a small drupe; flowers not racemed, mostly polygamo-dioecious; ovules pedulous.
Fam. 76. Ilicaceae. 2: 486. Seeds arilled; ovules erect; capsule fleshy. Fam. jj. Celastraceae. 2: 490.
Leaves simple and palmately veined, or compound. Leaves opposite.
Fruit a bladdery 3-lobed capsule. Fam. 78. Staphyleaceae. 2: 493.
Fruit of 2 winged samaras. Fam. 79. Aceraceae. 2: 494.
Fruit a leathery capsule; flowers irregular; leaves digitately compound.
Fam. 80. Aesculaceae. 2: 498. Leaves alternate; fruit various. Fam. 81. Sapindaceae. 2: 500.
tt Stamens as many as the sepals and alternate with them, opposite the petals when these are present; ovules erect.
Order 18. Rhamnales. Shrubs, small trees, or vines; petals 4 or 5, or none; fruit a drupe or capsule.
Fam. 82. Rhamnaceae. 2:501. Vines, climbing by tendrils, rarely shrubs; petals caducous; fruit a berry.
Fam. 83. Vitaceae. 2: 505.
** Stamens usually very numerous (except in some Hypericaceae, in Elatinaceae, Violaceae and Passifloraceae); disk inconspicuous or none.
t Sepals valvate; placentae united in the axis. Order 19. Malvales. Stamens in several sets; anthers 2-celled; embryo straight. Fam. 84. Tiliaceae. 2: 511.
Stamens monadelphous; anthers i-celled; embryo curved. Fam. 85. Malvaceae. 2:513.
tt Sepals or calyx-segments imbricated or convolute (except in Loasaceae, in which the calyx-tube is adnate to the ovary); placentae mainly parietal, sometimes united in the axis.
Order 20. Hypericales (Parietales). Sepals distinct, mostly persistent. Endosperm little or none.
Trees or shrubs with alternate leaves, and large solitary axillary flowers.
Farrr. 86. Theaceae. 2: 526. Herbs or low shrubs with opposite, rarely verticillate leaves.
Leaves stipulate; minute or small marsh or aquatic herbs with axillary flowers.
Fam. 88. Elatinaceae. 2: 537. Endosperm copious.
Flowers regular, but the 2 outer sepals smaller; stamens numerous; ovules orthotropous.
Fam. 89. Cistaceae. 2: 539. Flowers irregular, some often cleistogamous; stamens 5; ovules anatropous.
Fam. 90. Violaceae. 2: 545. Sepals more or less united into a gamosepalous calyx.