Flora of the Southeastern United States
2022 Edition

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Key to Rutaceae

1 Herbs, becoming somewhat woody at the base, < 1 (exceptionally to 1.4) m tall; [subfamily Rutoideae].
..2 Leaves 2-pinnatifid, with many segments; [alien, grown horticulturally, scattered as persistent or weakly naturalized]
..2 Leaves simple; [native in calcareous grasslands and woodlands in ne. and c. TX westwards and southwards]
1 Shrubs and trees, definitely woody, > 1 m tall when mature (flowering and fruiting).
....3 Leaves either simple, or unifoliolate and appearing simple.
......4 Stems unarmed, inflorescence axes and young stems with short, red-brown, scurfy hairs; inflorescences of short, compact to somewhat elongate racemes; [subfamily Aurantioideae; Bergera alliance]
......4 Stems armed or unarmed, inflorescences and young stems glabrous, or pubescent with short, grey to white, erect to curved hairs; inflorescences of small fascicles, or solitary or paired flowers; [subfamily Aurantioideae; Citrus alliance].
........5 Hesperidia bluish black when ripe, 0.8-1.2 cm in diameter; stamens 10; petiole not winged; stems armed; abaxial leaf surface with raised lateral veins; petals < 0.5 cm long
........5 Hesperidia green, yellow, or orange when ripe, > 1.5 cm in diameter; stamens 20+; petiole usually winged; stems armed or unarmed; abaxial leaf surface without raised lateral veins; petals > 1 cm long
....3 Leaves pinnately or palmately compound (1-foliolate leaves sometimes also present).
..........6 Leaves 1-pinnate, either odd-pinnate and (3-) 5-19-foliolate or even-pinnate and (4-) 6-8 (-14)-foliolate.
............ 7 Leaves opposite; stems and leaves unarmed.
............ ..8 Axillary buds concealed beneath the base of the petioles on mature, leafy stems; leaflets (7-) 9-13; bark on older stems corky; [subfamily Zanthoxyloideae]
............ ..8 Axillary buds exposed above the base of the leaf petioles on mature, leafy stems; leaflets 3-9 (-11); bark on older stems smooth to somewhat rough but never corky.
............ ....9 Fruit a drupe; diameter of mid-point of internodes of leafy branches usually 1-3 mm; internode lenticels usually < 0.3 mm long, mostly round (or absent); [native in FL and TX, and also planted and escaped in FL]; [subfamily Amyridoideae]
............ ....9 Fruit of 1-5 follicles; diameter of mid-point of internodes of leafy branches usually 3-6 mm; internode lenticels usually > 0.4 mm long and round to elongate; [planted and escaped in more northern parts of our area]; [subfamily Zanthoxyloideae]
............ 7 Leaves alternate; stems and leaves either unarmed, or armed with prickles.
............ ......10 Leaflets alternate on the rachis; fruit a berry, orange to red when ripe; stems and leaves unarmed; [subfamily Aurantioideae]
............ ......10 Leaflets opposite on the rachis; stems either not armed (Glycosmis) or stems (and also often leaves) armed with prickles (Zanthoxylum, except Z. flavum).
............ ........11 Fruit a berry; [subfamily Aurantioideae]
............ ........11 Fruit of 1-5 follicles; [subfamily Zanthoxyloideae]
..........6 Leaves palmately 3-foliolate.
............ ..........12 Branches armed with axillary spines; fruit a hesperidium; [subfamily Aurantioideae].
............ ............ 13 Petiole winged; stamens 20+; hesperidia 4-5 cm in diameter, dark yellow to orange when ripe, densely pubescent, usually with > 20 seeds (looking like a small, hairy orange)
............ ............ 13 Petiole not winged; stamens 6-10; hesperidia 1-1.5 cm in diameter, glabrous, red when ripe, with 1-4 seeds; spines usually paired at nodes; petals often 3
............ ..........12 Branches unarmed; fruit a drupe, few-seeded berry, or samara.
............ ............ ..14 Fruit a drupe or few-seeded berry; [subfamily Amyridoideae]
............ ............ ..14 Fruit a samara; [subfamily Zanthoxyloideae]

Key to Citrus

1 Leaves trifoliolate; fruit densely pubescent, 3-6 cm long
1 Leaves unifoliolate; fruit glabrous, 4.5-25 cm long.
..2 Petiole winged, and with an articulation at the juncture with the blade; fruit 4.5-15 cm long
..2 Petiole not winged, and lacking an articulation at the juncture with the blade; fruit 15-25 cm long