30 American Midland Naturalist Monograph No. 2 



2. Bud-scales not scurfy, paler; bundle-scars not forming a curved line; calyx usually 



5-Iobed; stamens 4-10, usually 8; fruit a pair of samaras 100. AcERACEAE 



1. Leaf-buds and leaf-scars alternate. 



3. Flowers (at least the staminate) in catkins, apetalous. 



4. Dioecious; ovary several-ovuled, 1-loculed; stigmas 2, often 2-lobed 



38. Salicaceae 



4. Monoecious. 



5. Styles or stigmas 3 (or 4) 42. Fagaceae 



5. Style 2-cleft, or stigmas 2 41. Betulaceae 



3. Flowers not m catkms. 



6. Branches with sharp stipular prickles; plants dioecious; sepals 0; petals 4-5, 



greenish yellow; stamens 4 or 5 ; pistils 2-5; leaves pinnate 



Zanthox^lum in 91 . RuTACEAE 



6. Branches not prickly; leaves simple. 



7. Flowers white (or pink), perfect; petals 5; sepals 5; stamens 15-25. 



8. Style 1 Prutius in 83. RosACEAE 



8. Styles 5 Amclanchier in 83. RosACEAE 



7. Flowers not white. 



9. Corolla papilionaceous, red-purple; flowers perfect, in umbel-like clusters; 



stamens 10; fruit a legume Cercis in 84. Leguminosae 



9. Corolla not papilionaceous; fruit not a legume. 



10. Corolla present, of 4 linear yellow petals; calyx 4-parted; stamens 8, 

 short; styles 2; fruit a capsule; flowers appearmg m autumn when 



the leaves are falling Hamamelis in 81. Hamamelidaceae 



10. Corolla none; flowers greenish, purplish, or yellowish, appearing in 

 spring. 

 1 1 . Flowers greenish or purplish; calyx 4-9-cleft; stamens 4-9, inserted 



on the calyx; styles 2; trees with serrate leaves 43. UlmacEAE 



11. Flowers yellowish or yellow; leaves entire. 



12. Calyx 6-parted; stamens 9, hypogynous; anthers opening by 

 valves; flowers fragrant, in small, sessile clusters; twigs with 



spicy odor and flavor Lindera in 68. Lauraceae 



12. Calyx tubular, corolla-like, obscurely 4-toothed 



111. Thymeleaceae 



Section 18. Ferns and Fern- Allies 



1. Plants attached to the substratum by roots, either growmg on land or submerged in 

 water, but not free-floating. 

 2. Leaves not quadnfoliolate or clover-like. 



3. Leaves narrow, sessile, 1 -veined, subulate or linear or oval, simple, not "fern- 

 like." 

 4. Leaves not whorled ; stem solid, not conspicuously jointed. 

 5. Stems elongated, leafy. 



6. Cones terete (or m some species the sporangia borne in the axils of ordin- 

 ary leaves); spores of only one kind, small; leaves without a ligule 



1. Lycopodiaceae 



6. Cones more or less 4-angled; spores of two kinds, large (megaspores), 

 and small (microspores), borne in different sporangia in the same cone; 



ligule present 2. Selaginellaceae 



5. Stem short, thick, corm-like; leaves rush-like, in a basal tuft; plants 



aquatic or growing in wet soil 3. IsOETACEAE 



4. Leaves whorled, united to form toothed sheaths at the conspicuous nodes on 



grooved, usually hollow stems; sporangia in a terminal cone 



4. Equisetaceae 



3. Leaves usually broad and "fern-like" in most spyecies, petiolate, often compound, 



with numerous or several free (rarely netted) veins. 



7. Small delicate ferns with filmy translucent leaves usually consisting of a single 



layer of cells; sporangia sessile on a filiform receptacle within a tubular or 



urceolate indusium 5. Hymenophyli.aceae 



