Podostemaceae is closely related to Clusiaceae or sister to Hypericaceae of the order Malpighiales in the rosids I. It is divided into 3 subfamilies, of which Podostemoideae and Weddellinoideae are more closely related to each other than to Tristichoideae. Tristichoideae retain relatively primitive characters.
Roots subcylindrical or ribbon-like, or root absent. Shoots cylindrical and ramified or crustaceous. Leaves flattened, oblong or ovate, univeined. Flower buds protected by membraneous bracts or cupules. Flowers 3-merous, perianths 3-lobed, stamens 1--3, ovary 1, 3-locular, stigmas 3. Capsules obtetrahedoral, 9-ribbed. 6 genera; 5 in Asia and Australia.
References: Cusset & Cusset (1988a, c), Cook (1996), Jäger-Zürn (1997), Rutishauser (1997), Kato (2006), Cook & Rutishauser (2007).
Root absent. Shoots crustose, with leaves on upper surface and margin. Rosettes with narrow leaves scattered on upper surface of old portions of shoots. Flower buds enclosed by cupules with filiform leaves. Flowers 3-merous. 6 species.
References: Jäger-Zürn (1995), Imaichi et al. (2004), Kato (2006)
Distribution: Thailand, S India, and Sri Lanka.
Roots ribbon-like. Reproductive shoot complex on flanks of root, comprising 2--3 branches, vegetative or floriferous, with leaves many, in 6 ranks, carinate on abaxial side. Flowers 3-merous. 2 species.
Distribution: Cambodia, Laos, and Thailand.References: Cusset (1973), Kato (2006).
Roots ribbon-like. Reproductive shoot complexes on flanks of root, each comprising 1 floriferous and 1 or few vegetative branches. Flowering shoots short; bracts 2 or several, membranous. 6 species.
Distribution: E China, Thailand, peninsular Malaysia, and NW Australia.References: Chao (1948, 1980), Dransfield & Whitmore (1970), Cusset & Cusset (1988), Imaichi et al. (1999), Kato et al. (2003), Kita & Kato (2005), Kato (2006)
Comprises 2 distinct species. In I. ramosissima, roots subcylindrical. Shoots on flanks of root, cylindrical, large, repeatedly ramified. In I. tirunelveliana, root absent. Shoots broadly ribbon-like, bearing ramuli. Ramuli short with 4-stichous leaves. In both, flowers 3-merous.
Distribution: S India.
References: Sharma et al. (1974), Rutishauser & Huber (1991), Jäger-Zürn (1992), Uniyal (1999).
Roots subcylindrical. Shoots on flanks of root, broadly ribbon-like, with leaves on upper surface and at margin. Flowers 3-merous. 1 species (originally Dalzellia gracilis).
Distribution: S India.
References: Mathew et al. (2001), Koi et al. (2009).
Roots subcylindrical. Shoots cylindrical, consisting of primary and secondary branches in 2 orthostichies, showing sympodial appearance, bearing scaly leaves and tufts of filaments. Pedicels with bracteoles. Flowers bearing 5 tepals, 5--25 stamens, 1 incompletely-bilocular ovary with 1 style and stigma. 1 genus and 1 species in South America.
References: Jäger-Zürn (1997), Rutishauser (1997), Koi & Kato (2007).
Roots subcylindrical, ribbon-like or crustaceous, or absent in some species. Shoots elongate or reduced. Leaves filiform, terete or unifacial, non-veined. Bracts simple, lobed or digitate. Flower buds enclosed by spathellas. Flowers 2-merous, tepals 2, filiform on either side of stamen or andropod, stamens 1--2 or multiple, ovary 1, 2-locular, sometimes 1-locular, stigmas 2. Capsules globose or ellipsoid and flattened, smooth or ribbed. Ca. 45 genera; 16 genera in Asia and Australia.
References: Cusset (1992), Cook (1996), Jäger-Zürn (1997), Rutishauser (1997), Kato (2004, 2006), Cook & Rutishauser (2007).
Roots subcylindrical or ribbon-like. Shoots reduced or elongate. Leaves filiform. Bracts simple. Flowers 2-merous. Stamens 1 or 2. Capsules ellipsoid, slightly flattened, ribbed. 15 species.
Distribution: S and N India, SE Myanmar, Thailand, N Laos, SW Cambodia.
References: Cusset (1992), Mathew & Satheesh (1997).
Roots narrowly ribbon-like. Holdfast on ventral side of root. Shoots reduced, on flanks of root between root branches and at sinuses of root branches. Bracts trifid with elongate middle lobe or digitate. Capsules globose, smooth or ellipsoid, ribbed. 2 species.
Distribution: Thailand
References: Kato (2006), Koi et al. (2008).
Root subcylindrical or ribbon-like. Holdfast absent. Vegetative and flowering shoots only at sinuses of root branches. Bracts 3--4-lobed or digitate; capsules globose, smooth. Ca. 10 species.
Distribution: SE and E Asia.References: Cusset (1992), Kato & Kita (2003), Kita & Kato (2003), Koi & Kato (2003), Kato (2006, 2008a, b, in press), Koi et al. (2005).
Root crustose. Shoots scattered on upper surface of root. Bracts in 4 ranks, dimorphic, ventral bracts (facing root) bilobed, dorsals simple. Flowers 2-merous. Capsules ellipsoid, ribbed. 2 species.
Distribution: Thailand.References: Cusset (1992), Kato (2006).
Root crustose. Shoots scattered on upper surface of root. Bracts in 2 ranks, trilobed with middle lobe much longer than laterals. Flowers 2-merous. Capsules ellipsoid, ribbed. 1 species.
Distribution: Thailand.References: Kato et al. (2004), Kato (2006).
Root crustose with shoots scattered on upper surface, or subcylindrical or ribbon-like with shoots on flanks. Bracts simple. Stamens 1 or 2. Capsules ellipsoid, ribbed. Ca. 12 species.
Distribution: Himalayas, SE and E Asia.References: Cusset (1992), Kita & Kato (2003), Kato & Kita (2003), Kato (2004), Kato (2008).
Roots various, stamens 1 or 2, capsules globose or ellipsoid, smooth. Roots subcylindrical or ribbon-like. Shoots on flanks of root. Bracts simple. Stamens 1. Capsules ellipsoid, ribbed. 2 species.
Distribution: S India and Sri Lanka.References: Cusset (1992), Mathew & Satheesh (1997).
Roots ribbon-like. Shoots on flanks of root. Bracts simple. Stamens 2. Capsules ellipsoid, flattened, valves unequal. 1 species.
Distribution: S India.References: Cusset (1992), Mathew & Satheesh (1997), Sehgal et al. (2002).
Roots disk-like. Holdfast in center of root on venral side. Shoots along margin of root. Bracts simple. Stamens 2. Capsules globose, smooth. 1 species.
Distribution: S India.References: Cusset (1992), Mathew & Satheesh (1997).
Roots crustaceous. Shoots on upper surface of root, elongate. Bracts 4- or 6-stichous, deltoid, simple or with elongate hair between 2 apical teeth. Capsules ellipsoid or subspherical, valves unequal, 2-ribbed. 2 species.
Distribution: S India.References: Cusset (1992), Mathew & Satheesh (1997), Shivamurthey & Sadanand (1997), Uniyal & Mohan Ram (2001).
Roots subcylindrical or ribbon-like with shoots on flanks, or crustaceous with shoots scattered on upper surface. Shoots reduced or elongate. Bracts simple. Flowers single or plural per shoot. Stamens 1 or 2. Capsule valves unequal, ribbed. 5 species.
Distribution: S and N India, Sri Lanka, Myanmar, N Thailand.References: Cusset (1992), Jäger-Zürn (1999, 2000a, b), Hiyama et al. (2002), Imaichi et al. (2005).
Diplobryum p.p. = Hydrobryum (S. Koi and M. Kato, in prep.)
Diplobryum p.p. = a new genus (S. Koi and M. Kato, in prep.)
Malaccotristicha = Terniopsis (Kato, 2006)
Polypleurella = Polypleurum (Kato, 2006)
Synstylis = Hydrobryum (Kato, 2004)
Tristicha in Australia (Tristicha australis) = Terniopsis australis (Kato, 2006)