Podostemaceae Rich. ex Kunth

Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://creativecommons.org/licenses/by/3.0

Morphology General Habit

Annual or perennial herbs, firmly attached to rocks and other solid substrates in seasonally strong currents of rivers and streams

Morphology Roots

Roots linear, prostrate and flattened, green, branched or not, or roots lacking

Morphology Stem

Stems prostrate, tightly attached to substrate throughout its length or arising along flanks of roots, opposite or sub-opposite, disk-shaped (holdfast-like) or upright

Morphology Leaves

Leaves distichous or tristichous, arising from stem margins, 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; when divided, ultimate divisions hair-like or flattened, blunt or acute at apex

Morphology Reproductive morphology Flowers

Flowers bisexual, solitary, fascicled or in 2-sided spiciform monochasia, pedunculate or not; actinomorphic or zygomorphic; enclosed in  sac-like spathella or spathella lacking; tepals 0-20, in complete or incomplete whorl, free or fused basally, linear, lanceolate or triangular; stamens 1-40, free or fused basally, in 1-2 complete whorls, or confined to one side of flower, or borne at apex of andropodium; filaments elongating during anthesis (most common) or not, anthers basifixed, dehiscing introrsely,  latrorsely or extorsely; pollen in monads, dyads or tetrads, tricolporate, tricolpate or pantopate; ovary 2-3-carpellate superior, sometimes borne on a short gynophore   at anthesis; placenta fleshy, axillary; ovules axile, anatropous, bitegmic, tenuinucellate; stigmas 1-2-3, free or fused basally

Morphology Reproductive morphology Fruits

Fruits capsular, 1-3-locular, 2-3-valved, septifragal longitudinally, smooth, ribbed or keeled, equal or unequal valves, both valves persistent or one deciduous; suture margins thickened or not; pedicel elongating (most common) in fruit or not; seeds ca. 1-2 mm long, numerous, becoming sticky upon wetting, without endosperm; embryo straight.

Note

Notes on delimitation: Historically the family was placed in the monotypic order Podostemales by Engler (1964), Cronquist (1981) and Takhtajan (1969). In the first version of the classification of the angiosperms given by the Angiosperm Phylogeny Group (1998), the family was left apart in an uncertain position. In the second version (APG II, 2003) Podostemaceae was assigned to Malpighiales related to Clusiaceae and Bonnetiaceae. In the latest version (APG III, 2009) a close relationship with Hypericaceae (formerly a part of Clusiaceae) was confirmed. Number of genera: There are twenty genera in the Neotropics (see above).

Diagnostic

Distinguishing characters (always present): Plants grow attached tightly to rocks or other solid substrates in strong currents of river-rapids and waterfalls, usually in sunny places. Flowering and seed production occur when plants become exposed during seasonally low water levels. Apinagia and Marathrum are difficult to distinguish. Apinagia has some species with prostrate stems while Marathrum has all species with prostrate stems. Both genera are polyphyletic (Tippery et al., pers. comm.). Castelnavia - when exposed in the air it looks like a lichen (a white spot in the rock), ovary surrounded by stem tissue during and after anthesis, asymmetrically inflated pedicelapex, anisolobous ovary perpendicular to pedicelaxis, unilocular mature capsule, and one deciduous capsule valve. Ceratolacis - presence of andropodium, stigma triangular becoming hardened and persisting in fruit, capsule slightly flattened. Cipoia - presence of gynophore at anthesis, ovary enclosed within ruptured spathella during and after anthesis, capsule enclosed by ruptured spathella, single stamen per flower. Diamantina - digitate leaves, gynophore at anthesis. Jenmaniella - presence of a gynophore at anthesis. Lonchostephus   - stamen filaments distinctly widened and flat. Lophogyne - flattened, irregularly dentate stigma s. Macarenia   - many flowers inside spathella. Monostylis - presence of a gynophore at anthesis, capsules elongate and flattened, each capsule valve with 5 non-suture ribs per valve. Mourera - rough leaves, often with showy two sided spike-like monochasial inflorescence. Oserya - South American species with prostratestem, 3 tepals per flower, 5 non-suture ribs per capsule valve; Mexican species with upright stem, 2 tepals per flower, 5 non-suture ribs per capsule valve. Podostemum - distinct stipules persistent on old stems, pollen in dyads, presence of andropodium. Rhyncholacis - flowers in fascicles arising from prostratestem, flattened capsules with midrib extensions on both sides that are contiguous with the persistent rigid styles. Tulasneantha - stamen filaments united for half their length forming an androecial tube. Tristicha - moss-like appearance, tristichous leaves, trimerous flower and fruit. Vanroyenella - plumose leaves, induratestamen filaments. Weddellina - flowering stems short (< 2 cm) and unbranched, vegetative stems to ca. 1 m long and branched, vegetative stems with reduced scale-like leaves, spathella lacking, style one, stigma globose. Wettsteiniola - flowers in fascicles, fruits with 5 ribs per valve. Key differences from similar families: There are no similar families in the Neotropics. Remarkably variable in form.  Some lichen- or algae-like in overall appearance. Presence of a sac-like cover (spathella) that encloses the young flower (absent in Tristicha and Weddellina).

Distribution

Only native taxa are found. Worldwide Podostemaceae comprise ca. 50 genera and approximately 270 species. About 20 genera and 150 species occur in the Neotropics. The family is pantropical with a few species extending into temperate eastern Asia and eastern North America. In the Neotropics it ranges from central Mexico to northern Paraguay and Argentina. Apinagia Tul. - about 50 species, Colombia to Paraguay and Uruguay, mainly in Guiana and Brazil Shields. Castelnavia Tul. & Wedd. - six species, central and southeastern Brazil to eastern Bolivia. Ceratolacis (Tul.) Wedd. - two species, endemic to central Brazil. Cipoia C.T.Philbrick, Novelo & Irgang - two species, endemic to southeastern Brazil. Diamantina Novelo, C.T. Philbrick & Irgang - monospecific (D. lombardii Novelo, C.T. Philbrick & Irgang), endemic to southeastern Brazil. Jenmaniella Engl. - seven species in Guiana and Brazil Shields. Lonchostephus Tul. - monospecific (L. elegans Tul.), endemic to southeastern Brazil. Lophogyne Tul. - monospecific (formerly two species, recently put in synonymy (Bove et al. 2010), endemic to central Brazil. Macarenia P. Royen - monospecific (M. clavigera P. Royen), endemic to Colombia. Marathrum Humb. & Bonpl. - nine species, West Indies and southern Mexico through Central America to South America (Brazil, Guiana Shield, southern Paraguay and northern Argentina). Monostylis Tul. - monospecific (M. capillacea Tul.) endemic to central Brazil. Mourera Aubl. - six species, Colombia through Guiana Shield to Brazil, Paraguay and northern Argentina. Oserya Tul. & Wedd. - seven species, west-central Mexico, Venezuela, Guianas and northern Brazil.  Recent phylogenetic studies indicate the genus is not monophyletic (Tippery et al., pers. comm.). Podostemum Michx. - 11 species, eastern North America, central Mexico, Colombia, southeastern South America (Argentina, Brazil, Paraguay, Uruguay). Rhyncholacis Tul. - 22 species, northern South America. Tristicha Touars - one polymorphic species (T. trifaria (Bory ex Willd.) Spreng.), widely distributed in tropical and subtropical America, Africa and Asia. Tulasneantha P.Royen - monospecific (T. monoadelpha (Bong.) P. Royen), endemic to central Brazil. Vanroyenella - monospecific (V. plumosa Novelo & C.T. Philbrick).  Phylogenetic analyses (Tippery et al., pers. comm.) support transfer of V. plumosa into Marathrum. Weddellina (Warm.) Engl. - monospecific (W. squamulosa Tul.), northern South America (Guianas, Venezuela) and central Brazil. Wettsteiniola Suess. - three species, southern Brazil to northern Argentina and Paraguay.

Podostemaceae, C. Cusset. Flora Zambesiaca 9:2. 1997

Morphology Stem

Stems simple or with abbreviated side shoots, leafless to ± densely leafy, and/or with reduced leaflets on flowering branches, or stems suppressed

Morphology Leaves

Leaves linear to filiform or reduced and scale-like (moss-like); linear leaves floating, entire or dichotomously, pinnately or laciniately divided, exstipulate or sometimes with 2 tooth-like stipules; scale-like leaves when present 3-ranked (tristichous) or 2-ranked (distichous), scattered or absent on the stems, and ± densely imbricate on branches and flowering shoots

Morphology Reproductive morphology Flowers

Flower hermaphrodite, small, actinomorphic or zygomorphic, without a spathella, or with a persistent membranous spathella (2 spathaceous bracts); spathella at first encloses the flower-bud and at anthesis tears irregularly at the apex allowing the pedicel to elongate bearing the flower erect beyond the spathella; flower-bud subtended by 2–3 free protecting bracts, or flower-bud at first inverted (reflexed) within a membranous spathella (also erect within the spathella outside the Flora Zambesiaca area)

Morphology Reproductive morphology Flowers Perianth

Perianth of 3 segments (tepals) connate in their lower part, or perianth reduced to 2 minute free filiform structures, lateral to, and shorter than, the androecium, or perianth absent

Morphology Reproductive morphology Flowers Androecium

Stamens hypogynous, 1 or 2 with filaments connate for at least one-third of their length; anthers 2-locular, dehiscing introrsely by a longitudinal slit

Morphology Reproductive morphology Flowers Gynoecium

Ovary sessile or on a gynophore, globose to ellipsoid, 1–2 or 3-locular with locules of equal or unequal size; locules ellipsoid to fusiform or subglobose, 2-lobed or not, placentation central or axile, bearing numerous anatropous ovules; styles 2 or 3, sessile or subsessile, usually free, variable in shape

Morphology Reproductive morphology Fruits

Capsule brown, spherical to ellipsoid or fusiform, smooth or adorned with ± wide longitudinal ribs, dehiscing in dry air into 2–3 equal and sometimes caducous valves, or 2 unequal valves of which only the smaller is caducous

Morphology Reproductive morphology Seeds

Seeds reddish-brown to blackish, minute, slightly flattened-ellipsoid to ovoid, exalbuminous; testa reticulate; embryo straight

Morphology General Habit

Plants of this family are moss-like freshwater herbs, almost always found in swift-flowing, permanent rivers, usually in turbulent waters of cataracts and waterfalls, or in continuous water-spray, often firmly fixed to rocks by a lichen-like thalloid basal part. Submerged and often annual the plants flower as they become exposed to air when water levels recede. Pollination is usually by insects, or by wind. Fruits develop rapidly after pollination. The seed coat is mucilaginous when wet and adheres to the substrate where it germinates Submerged freshwater herbs, firmly attached to rocks and stones in swift-flowing water or spray of waterfalls, often resembling mosses, liverworts or algae, habit also adapting to depth of water and receding water levels Plant base usually thalloid, variable in form and bearing endogenous buds on the margins and surface from which flowering shoots and stems arise

Podostemaceae, H. J. Beentje, M.Sc., Ph.D., F.L.S.. Flora of Tropical East Africa. 2005

Morphology General Habit

Plant base usually thalloid, variable in form, without vessels, sometimes without xylem, bearing buds on the margins and surface from which shoots arise; thallus attached to the substrate by haptera, flattened disc-like organs excreting a cement-like substance, and sometimes with filiform rootlets; stem simple or with abbreviated side-shoots, sometimes suppressed Aquatic herbs, looking like mosses, lichens or algae and usually growing on rocks or stones submerged in fast-flowing water

Morphology Leaves

Leaves absent or, where present, alternate, entire to dissected, linear, filiform, or scale-like, 3-ranked or 2-ranked, sometimes densely imbricate on branches and flowering shoots; exstipulate or sometimes with 2 tooth-like stipules

Morphology Reproductive morphology Flowers

Flowers bisexual, regular or irregular, small, solitary or in cymes, sometimes cleistogamous; bracteoles 2, enclosing the flower (‘spathella’) and then tearing irregularly at anthesis allowing the pedicel to elongate beyond the spathella, or spathella absent and bracts subtending the flower; tepals absent or 2–3(–5), ± connate or free, or consisting of a small annular scale; stamens hypogynous, 1–2(–4), with the filaments usually at least basally connate, dehiscing introrsely with a longitudinal slit Flowers and fruits produced aerially at low water

Morphology Reproductive morphology Flowers Gynoecium

Ovary sessile or stalked, (1–)2(–3)-locular with as many ± basally connate (sub-)sessile stigmas; ovules many, anatropous, on thickened axile placentas

Morphology Reproductive morphology Fruits

Fruit a stalked capsule, smooth or ribbed, dehiscing into 2–3 valves in dry air; seeds usually many, very small, often with mucilaginous testa