Descripción de la familia por A. Novelo R., C.T. Philbrick y G.E. Crow.Annual or perennial herbs, firmly attached to rocks and other solid substrata of waterfalls and rivers and streams with seasonally strong current. Roots linear, prostrate and flattened, green, branched or not. Stems arising along the flanks of roots, opposite or sub-opposite, disk-shaped (holdfast-like) or upright, attached firmly to the substratum. Leaves distichous or tristichous, clustered and rosette-like or projecting from an upright stem, petiolate or sessile; petioles terete to flattened, sometimes winged, mono-or dithecous; blades variable, simple, lobed, repeatedly pinnately or dichotomously compound or ensiform, when divided, the ultimate divisions hairlike or flattened, blunt or acute at the apex. Flowers solitary or fascicled, pedunculate or not, actinomorphic or zygomorphic, enclosed in bud by a sac-like spathella or a spathella lacking; tepals 3-9, scale-like, free or fused basally, linear or triangular; stamens 2-11, free or fused basally, in a complete whorl , or confined to one side of flower, the filaments elongating during anthesis, the anthers basifixed, dehiscing introrsely or latrorsely; pollen in monads or dyads; ovary 2-3-locular, superior, the placenta fleshy; stigmas 2-3, apically free or fused basally. Capsules 2-3-locular, 2-3-valved, longitudinally ribed, both valves persistent or one deciduous, the suture margins often thickened or not; seeds tiny, numerous, becoming sticky upon wetting. 47 gen., approx. 270 spp. Pantropical, a few species extending into temperate eastern Asia and eastern North America.Plants grow attached tightly to rocks or other solid substrata in strong currents of riverrapids and waterfall habitats. Flowering and seed production occurs when plants become exposed during seasonally low water levels.Bibliografía [matted]. Leaves scale-like, arranged in ramuli, generally tristichous, sessile, membranous, nerveless or 1-nerved. Flowers solitary, bisexual, enclosed by 2 bracts in bud; pedicellate; tepals 3, persistent, usually united at the base; stamens 1(2), the filaments slender, the anthers basifixed, dehiscing introrsely or latrorsely; pollen in monads; ovary 3-locular; stigmas 3, free, cylindrical; ovules numerous, the placenta axile. Capsules with 3 equal valves, persistent, each valve 3-ribbed, the suture margins not thickened and rib-like; seeds numerous, dust-like. Perennials. Roots 0.3-1.2 mm wide, prostrate, linear. Stems 1-11 cm, ascending to procumbent, branched or simple. Leaves 0.6-7 × 0.4-0.9 mm, 3-ranked (tristichous), scale-like, the apex acute to rounded. Pedicels 0.15-1.5 cm; lowest floral bract at pedicel base 1.1-2.8 mm, the adjacent upper bract 1-2.6 mm. Tepals 3-lobed, 1.3-2 mm, united at the base; stamens 1(2), the filaments 0.8-1.9 mm, the anthers 0.3-0.9 mm; stigmas 0.2-0.7 mm. Capsules 1-2 × 0.7-1. Tristicha trifaria is the most common member of the family in the Americas, and appears to be fairly tolerant of stream pollution. Its moss-like appearance, however, contri...

Target two of the 2002 Global Strategy for Plant Conservation (GSPC), ''A preliminary assessment of the conservation status of all known plant species, at national, regional, and international levels'' was not accomplished by its original 2010 target date and has therefore been included as a revised 2020 target, ''An assessment of the conservation status of all known plant species, as far as possible, to guide conservation action.'' The most widely used system to estimate risk of extinction, the International Union for the Conservation of Nature Red List, provides conservation assessments for fewer than 15,000 plant species. Progress achieving Target two has been hampered by the large number of plant species and the difficulty assembling the data needed for Red List assessments. Two streamlined methods for identifying those plant species considered At Risk under the GSPC Target two are compared and contrasted. Both methods use readily available locality data from herbarium specimens to efficiently identify At Risk species and approximate the list of species that would be identified as threatened by Red List analyses. A comprehensive analysis of the native plant species of Puerto Rico using both streamlined methods identifies 570 of the 2,025 species at some risk of extinction. More efficient systems for assessing threat allow a more timely response to Target two, allow conservation efforts to be directed to the species that need attention, and the list of threatened plants can be used to identify priority areas for plant conservation.

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Target 2 of the 2020 Global Strategy for Plant Conservation (GSPC) calls for a comprehensive list of the world's threatened plant species. The lack of such a list is one of the greatest impediments to protecting the full complement of the world's plant species, and work to achieve this has been slow. An efficient system for identifying those species that are at risk of extinction could help to achieve this goal in a timeframe sensitive to today's conservation needs. Two systems that efficiently use available data to assess conservation status were tested against a provisional International Union for Conservation of Nature and Natural Resources (IUCN) Red List analysis to evaluate the native seed plant species of Puerto Rico. It was demonstrated that both systems efficiently identify species at risk, which is a step toward both the GSPC Target 2 and a more comprehensive IUCN Red List for plants. Both systems were effective at identifying plant species at risk, with the New York analysis identifying 98% and the Smithsonian analysis 85% of the plant species considered Threatened in the IUCN Red List. Both analyses to some extent overestimated those plants at risk, but the species identified are all range restricted and, thus, of some conservation interest.

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