Burger, W. 1983. Flora Costaricensis: Podostemaceae. Fieldiana Botany,

N.S. 13: 1-8.

Cook, C. D. K. 1990. The Aquatic Plant Book. The Hague. SPB

Academic Publishing.

Novelo R., A. and C. T. Philbrick. 1997. Taxonomy of the Mexican

Podostemaceae. Aquat. Bot. 57:275-303.

Novelo R., A. and C. T. Philbrick. 1997. Podostemum ricciiforme (Podostemaceae) rediscovered

and redescribed. Taxon 46: 451-455.

Philbrick, C. T. and A. Novelo R. 1995. New world Podostemaceae:

ecological and evolutionary enigmas. Brittonia 47: 210-222.

van Royen, P. 1951. The Podostemaceae of the New World. Part I.

Meded. Bot. Mus. Herb. Rijks Univ. Utrecht 107: 1-151.

van Royen, P. 1953. The Podostemaceae of the New World. Part II. Acta

Bot. Neerl. 2: 1-21.

van Royen, P. 1954. The Podostemaceae of the New World. Part III. Acta

Bot. Neerl. 3: 215-263.

47 gen., ca. 270 spp. Pantropical, few species extending into temperate e. Asia and e. North America; 2 gen., 4 spp. in CR.

Annual or perennial. Submersed herbs of waterfalls, freshwater rapids, and fast moving streams with a rocky bottom, growing attached chiefly to rocks by specialized photosynthetic roots modified as firmly attached creeping slender ribbon-like structures (haptera) and/or thalloid holdfasts (often lichen-like or fucoid). Stems difficult to distinguish from roots. Leaves typically arising from holdfasts (borne along stem in Tristica), varying greatly among different genera and within species, entire to nearly so, but often repeatedly branched, absent in some. Flowers developing as the water level drops, typically at anthesis near water edge, elevated in air, cleistogamous in some species. Flowers solitary or in fascicles, or in cymose (often spiciform) inflorescences, typically each flower initially enclosed by a membranous spathella, or spathella absent. Flowers small, elevated by elongate pedicels, bisexual. Perianth (tepals) present, 2—5, free or united at base, or sometimes reduced to scale-like tepals. Stamens 1-many, borne in 1-2 whorls, or in 1 incomplete whorl, or restricted to one side of flower. Filaments free or in some genera with filaments inserted on a distinct stalk (andropodium). Pollen dispersed as monads, diads, or clumped. Ovary superior, 1- to 3-locular. Fruit a capsule, dehiscing to base, often one valve readily falling away. Seeds 2—numerous, usually tiny, testa becoming mucilaginous in contact with wet substrate, readily sticking to rocks.

1. Plants resembling bryophytes (typically forming a dense low mat on rock face); leaves entire, very small, scale-like, usually less than 2 mm long, imbricate on elongate stem, 3-ranked; stamens 1 (rarely 2); ovary 3-locular, stigmas 3; capsules with 3 valves…Tristica

1. Plants not resembling bryophytes; leaves various, lamina broad and somewhat lobed (at least toward apex) to much divided; much larger (mature leaves several cm long), not imbricate, arising from holdfast; stamens 2—9 (-10); ovary 2-locular, stigmas 2; capsules with 2 valves.

2. Prostrate axis more than 3 mm in diameter; stamens 2-9(10) with anthers separate, not on an andropodium; pollen in monads…Marathrum

2. Prostrate axis less than 3 mm in diameter; stamens 2, filaments borne on an andropodium; pollen in dyads…Podostemum

Annual or perennial. Attached to rocks by broad thalloid holdfast. Leaves very variable, arising from the holdfast; petiole terete or somewhat flattened; blade repeatedly forked or pinnately divided, with pinnae alternate or subopposite, or nearly entire, with few lobes along the margin (at least at toward apex). Flowers bisexual actinomorphic or slightly zygomorphic (stamens and perianth on one side), borne singly or in fascicles, initially enclosed in a spathella. Pedicels slender, elongate, elevating the flower above the water line, sometimes expanded to form a cup-like structure at apex. Perianth (tepals) scale-like, free or united at base, sometimes inserted on the cup-like pedicel apex. Stamens 2—10 (-25), filaments free, alternating with tepals, in a whorl or on only side of pistil. Pollen shed in monads. Ovary superior, 2-carpellate, styles 2. Fruit a capsule, dehiscing to base along ribs, valves 2, subequal, each with 5 ribs, one valve readily deciduous, the other long persisting. Seeds numerous, tiny.

Ca. 25 spp., neotropics from Mexico and Cent. Amer. to northeastern S. Am.; Antilles; 3 spp. reported for CR.

1. Leaves not divided, entire or frequently somewhat irregularly lobed or toothed toward apex, tapering toward base; blade relatively broad, 2—30 (-60) mm wide, venation dichotomous and ultimately reticulate (conspicuous in dried specimens)…M. utile

1. Leaves repeatedly divided, with distinct petiole and rachis; blade divisions nearly filiform; veins indistinct or appearing absent.

2. Divisions of leaves alternate, ultimate divisions thicker, usually 1—3 mm wide, not readily collapsing out of water; flowers actinomorphic, stamens and perianth (6-) 7—9 (-10)…M. schiedeanum

2. Divisions of leaves subopposite, ultimate divisions very slender, filiform, flattened, up to 0.2 mm wide, appearing as clusters, readily collapsing when out of water; flowers slightly zygomorphic, stamens and perianth 2—3, borne on one side of flower…M. tenue

Marathrum schiedeanum (Cham.) Tulasne, Ann. Sci. Nat., ser. 3, 11: 95. 1849. Lacis schiedeanum Cham., Linnaea 9: 504. Tab. VI. 1835. M. flexuosum Leibm., Forhandl. Skand. Naturf., Copenhagen 5: 511. 1847. M. haenkeanum Engler, in Engler Bot. Jahrb., 61 Beibl., Nr. 138: 4. 1928. M. elegans van Royen, Meded. Bot. Mus. Herb. Rijks Univ. Utrecht 107: 131. 1951.

Additional images of M. schiedianum

 

Marathrum tenue Liebm., Forhandl. Skand. Naturf., Copenhagen 5: 11. 1847. Neolacis myriophylla Weddell, in DC., Prodromus 17: 63-64. 1873. Blandowia myriophylla (Weddell) Nash, N. Amer. Fl. 22, pt. 1: 5. 1905. Apinagia myriophylla (Weddell) Engler, Die Natur. Pflanzen. 18a: 18. 1930. Marathrum kerberi Engler, in Engler Bot. Jahrb. Syst., 61 Beibl., Nr. 138: 5. 1927.

Drawing from Burger, 1983: Flora Costaricensis

Additional image of M. tenue

Marathrum utile Tulasne, Ann. Sci. Nat. (Paris), ser. 3, 11: 95. 1849.

 

Drawing from Burger, 1983: Flora Costaricensis

 

Perennial. Prostrate axis (roots) slender, flattened, usually branched, firmly attached to rocks in rapids. Stems arising from alternate sides of creeping axis, distinct or obscured. Leaves in 2 rows, distichous, linear, entire or repeatedly forked, with intrapetiolar stipule usually present, especially upper leaves. Flowers bisexual, slightly zygomorphic (stamens and perianth on one side). Tepals 3, scale-like, 2 borne at base of andropodium and 1 at the top of the andropodium at the fork of the 2 filaments. Stamens 2, borne on an andropodium arising from one side of pistil. Pollen shed in dyads. Ovary superior, 2-carpellate, styles 2. Fruit a capsule, with 6-8 ribs, dehiscing by 2 unequal valves, the larger persistent, the smaller readily caducous. Seeds numerous, tiny.

Podostemum ricciiforme (Liebm.) P. Royen, Acta Bot. Neerl. 3(2): 240. 1954.

One specimen from Costa Rica, Endres 181(W), was cited by van Royen (1954) as belonging to P. ricciiforme. However, in a detailed study of the Podostemaceae of Mexico, Novelo and Philbrick (1997a,b) note that the Endres 181 specimen included in this species by van Royen was misidentified, or at least do not include it within their concept of the species. They consider the P. ricciiforme to be endemic to the Atlantic slope of Mexico. [Unfortunately, they do not, in print, provide an indentity for our Costa Rican material. Philbrick (personal communication) indicates that it certainly has affinities with P. ricciiforme, but the Costa Rican specimen represents a larger plant than the Mexican material--Novelo is inclined to consider it a new species. While the Endres 181 specimen does not have specific locality information on the label, I will be looking for Podostemum on the Atlantic slope in the region near Cahuita and Bribri. I was in the field with Novelo and Philbrick when P. ricciiforme was rediscovered in Mexico, and have a good feel what to look for in Costa Rica].

Drawing from Novelo & Philbrick, 1997: Taxonomy of Mexican Podostemaceae

Drawn from Endres 181(W), Costa Rica (by G. Crow)

Perennial. Small aquatic herbs appearing like bryophytes, forming dense mats on rocks in fast-moving streams. Stems slender, simple or branched, typically short and creeping, but sometimes up to 11 cm long (then trailing into current). Leaves alternate, very small, scale-like, typically less than 2 mm long (up to 7 mm), imbricate, 3-ranked. Flowers solitary, terminal or on short lateral branches, enveloped in leaves when young. Spathella absent. Perianth segments 3, free or united at base. Stamens 1 (rarely 2). Ovary 3-locular, stigmas 3. Fruit an ovoid to ellipsoid capsule, 1—2 mm long, with 9 conspicuous ribs, dehiscing by 3 valves. Seeds tiny.

2 spp., neotropics, Africa, and Madagascar; 1 sp. in New World.

Tristicha trifaria (Bory ex Willd.) Sprengel, Syst. Veg., ed. 16, 1: 22. 1825. Dufourea trifaria Bory ex Willd., Sp. Pl., ed. 5: 55. 1811. Tristicha hypnoides (St. Hil.) Sprengel, Syst. Veg. 4, pt. 2: 10. 1827.

Preliminary Draft: 20 February, 1998