Part 1, 1909] ZANNICHELLIACEAE 23 
23. Potamogeton latifolius (Robb.) Morong, Mem. Torrey 
Club 3’: 52. 1893. 
Potamogeton pectinatus latifolius Robb. in S. Wats. Bot. King’s Expl. 338. 1871. 
Stem whitish, branched ; leaves all submerged, linear, with an acute or obtuse apex, 
2.5~7 cm. long, 2-2.5 mm. wide; primary nerves 3-5 with numerous reticulated cross-nerves ; 
stipules adnate to the leaf-bases, scarious, the sheath 1-2.5 cm. long, the free part shorter ; 
spikes cylindric, 2-3 cm. long, interrupted below; peduncles whitish, thinner than the 
stem, 2.5-8 cm. long; nutlets smooth, mostly without keels, rarely with one inconspic- 
uous keel; embryo a complete spiral, the curved apex pointing inside the base. 
TYPE LOCALITY: Humboldt Mountains, Nevada. 
DISTRIBUTION : Northwestern Nevada and northeastern California, 
ILLUSTRATIONS: Mem. Torrey Club 3?: £7. 59. 
24. Potamogeton Robbinsii Oakes, Mag. Hort. Hovey 7: 180. 1841. 
Stem slender, branched and sometimes rooting at the nodes; leaves all submerged, 
linear, minutely serrulate throughout, 8-13 cm. long, 2.5-4 mm. wide, apiculate or acute 
at the apex, somewhat clasping at the base, many-nerved ; stipules adnate tothe leaf-bases, 
the sheath 1-1.5 cm. long, the free part longer; peduncles 3-10 cm. long, usually branched, 
a little thinner than the stem ; spike slender, 1-2 cm. long, many-flowered but sparingly- 
fruited; nutlets slightly pitted, 3-keeled, the middle keel larger than the lateral ones; 
embryo a complete or incomplete spiral, the apex pointing directly towards the base or 
inside it. 
TYPE LOCALITY: New Hampshire. 
DISTRIBUTION: Maine to British Columbia, south to Pennsylvania, and Washington. 
ILLUSTRATIONS: Mem. Torrey Club 3?: /. 67; Britt. & Brown, Il. Fl. f. 175. 
25. Potamogeton interruptus Kit.; Schultes, Oestr. F1. 
ed. 2.1: 328. 1814. 
Péiamogeton fiabellatus Bab. Man. Bot. ed. 3. 343. 1851. 
Potamogeton pectinatus interruptus Aschers. Fl. Brand. 1: 666. 1864. 
Stem whitish, branched ; leaves all submerged, linear, entire, 2~8.5 cm. long, 1-1.5 mm. 
wide, acute, acuminate or obtuse at the apex; primary nerves 1-5, rarely with a fewcross- 
nerves; stipules adnate to the leaf-bases, the sheath 1-2 cm. long and not scarious except 
on the edges, the free part shorter, scarious ; spikes 24.5 cm. long, interrupted, the flower 
clusters often 1 cm. apart; peduncles whitish, thinner than the stem, 3-7 cm. long; nutlets 
3-keeled, the middle keel larger than the lateral ones; embryo a complete or incomplete 
spiral, the apex pointing towards or inside the base. 
TYPE LOCALITY: Hungary. . 
DISTRIBUTION : Michigan, Wisconsin, Nebraska, and Saskatchewan ; apparently in Guatemala. 
ILLUSTRATIONS: Mem. Torrey Club 3?: £2. 60; Britt. & Brown, Ill, Fl. f. 174. 
John Donnell Smith 4076, from Guatemala, upon which Ascherson and Graebner (Pflanzen- 
reich 411: 169) base the occurrence of P. striatus in North America, is apparently the above; 
mature fruit is unknown. 
26. Potamogeton pectinatus L,. Sp. Pl.127. 1753. 
Potamogeton angustissimus H.B.K. Nov. Gen. & Sp. 1: 370. 1815. 
Potamogeion pectinatus scoparius Wallr. Sched. Crit. 68. 1822. 
Stem slender, much branched; leaves all submerged, capillary, often fasciculate, 2-15 
em. long, 0.1-0.3 mm. wide, with a more or less pungent point; stipules adnate to the 
leaf-bases, whitish, the sheath 1-2 cm. long, the free part shorter; spikes 1-3 cm. long, 
many-flowered, often interrupted; peduncles slender, 5-18 cm. long; nutlets at least 2.5 
mm. long, with 2 obscure lateral keels but no median one; style projecting at least 0.6 
mm. above the body of the fruit; embryo a complete or incomplete spiral, the apex point- 
ing directly towards the base or inside it. 
TYPE LOCALITY: Europe. . : 
DISTRIBUTION: Throughout North America, except Central America and the West Indies; 
reported, however, from Panama; also in Europe. 
POLLUSTRATIONS : Britt, & Brown, Ill, Fl. f. 173; Mem. Torrey Club 3?: p1. 58; Engler, Pflan- 
zenreich 4: 7. 28 a, 6. 
