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Key to Citrus

Rutaceae

Citrus

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1 Leaves trifoliolate; fruit densely pubescent, 3-6 cm long
1 Leaves unifoliolate; fruit glabrous, 4.5-25 cm long (except ca. 2.5-5 cm long in C. japonica, which has glabrous fruit).
  2 Ovary with 3- or 4-locular (rarely 6), each of these bearing 3 or 4 ovule
  2 Ovary with (6-) 7-15 locule, each with many ovule.
    3 Petiole not winged, and lacking an articulation at the juncture with the blade; fruit 15-25 cm long, the rind (exocarp) wider than the pulp (mesocarp)
    3 Petiole winged (except C. reticulata, which sometimes lacks wings entirely), and with an articulation at the juncture with the blade; fruit 4.5-15 cm long
      4 Outer petal surfaces and flower buds pink or purple tinged.
        5 Petiole slightly margined; fruit apex with a prominent nipple
        5 Petiole BLANK; fruit apex with a truncate or depressed, sunken nipple
      4 Outer petal surfaces and flower buds white or cream-colored.
          6 Flowers ≤ 25 mm wide, the petal 8-12 mm long; the fruit ≤ 4(-5) cm wide.
             7 Mature fruit with an apical nipple, the rinds green to yellow
             7 Mature fruit with an apical nipple, the rinds orange
          6 Flowers ≥ 25 mm wide, the petal 14-25 mm long; the fruit 3-15 cm wide.
               8 Petiole wings absent, or only present on one side (subequal to or narrower than the petiole width); rinds (exocarp) 1-4 mm thick, not readily adherent and easily separated from the mesocarp (pulp)
               8 Petiole wing on one side usually subequal to wider than the width of the petiole; rinds (exocarp) 5-12 mm thick, adherent and not easily separated from the mesocarp (pulp).

Key to Rutaceae

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1 Herbs, becoming somewhat woody at the base, < 1 (exceptionally to 1.4) m tall; [subfamily Rutoideae].
  2 Leaves 2-pinnatifid, with many segment; [exotic, 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 hair; inflorescence of short, compact to somewhat elongate raceme; [subfamily Aurantioideae; Bergera alliance]
      4 Stems armed or unarmed, inflorescence and young stems glabrous, or pubescent with short, grey to white, erect to curved hair; inflorescence of small fascicle, or solitary or paired flowers; [subfamily Aurantioideae; Citrus alliance].
        5 Hesperidia bluish black when ripe, 0.8-1.2 cm in diameter; stamen 10; petiole not winged; stems armed; abaxial leaf surface with raised lateral veins; petal < 0.5 cm long
        5 Hesperidia green, yellow, or orange when ripe, > 1.5 cm in diameter; stamen 20+; petiole usually winged; stems armed or unarmed; abaxial leaf surface without raised lateral veins; petal > 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 bud concealed beneath the base of the petiole on mature, leafy stems; leaflet (7-) 9-13; bark on older stems corky; [subfamily Zanthoxyloideae]
               8 Axillary bud exposed above the base of the leaf petiole on mature, leafy stems; leaflet 3-9 (-11); bark on older stems smooth to somewhat rough but never corky.
                 9 Fruit a drupe; diameter of mid-point of internode of leafy branches usually 1-3 mm; internode lenticel 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 follicle; diameter of mid-point of internode of leafy branches usually 3-6 mm; internode lenticel 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 prickle.
                   10 Leaflet alternate on the rachis; fruit a berry, orange to red when ripe; stems and leaves unarmed; [subfamily Aurantioideae]
                   10 Leaflet opposite on the rachis; stems either not armed (Glycosmis) or stems (and also often leaves) armed with prickle (Zanthoxylum, except Z. flavum).
                     11 Fruit a berry; [subfamily Aurantioideae]
                     11 Fruit of 1-5 follicle; [subfamily Zanthoxyloideae]
          6 Leaves palmately 3-foliolate.
                       12 Branches armed with axillary spine; fruit a hesperidium; [subfamily Aurantioideae].
                          13 Petiole winged; stamen 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; stamen 6-10; hesperidia 1-1.5 cm in diameter, glabrous, red when ripe, with 1-4 seeds; spine usually paired at node; petal 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]