In order to elucidate the floral ontogeny of certain Thai species of the subfamily Podostemoideae the flowering shoots of Hanseniella heterophy/la Hydrobryum loeicum and Hy. tardhuangense were observed using scanning electron microscope. In all species studied. the flowering shoots protrude from the cavities where the tufted leaves arise on the crustose root. Mostly the two outer bracts are leaf-like interpreting that the flowering shoots are converted from the vegetative shoots. In Hanseniel/a bracts in the early developmental stage are similar shapes but different sizes arranging in 4 rows. In the mid-stage the ventral bracts differentiate into normally 2 lobes occasionally 3 lobes whereas the dorsal bracts develop into long deltoid shape. In Hydrobryum the arrangement of bracts is distichous. The spathellas in all species initiate from tissue surrounding the floral meristem. Prior to the fusion of ventral and dorsal apical margins the spathella apices become a triangle space in Hanseniella narrow long space in Hy. loeicum and two-lipped in Hy. tardhuangense; and the floral organs are initiated inside the spathella. The two tepal primordia the primary androecial primordium and the gynoecial primordium are initiated simultaneously. The two stamen primordia are differentiated from the primary androcial primordium when the gynoecium changes into a cylindrical shape and two carpel primordia are initiated. These dramatic ontogenetic changes and heterochronic shifts in the initiation of floral organs are highly specialized and very distinct floral development which have not found in any families of flowering plants.

The species composition of Podostemaceae was studied in Loei northeastern Thailand from November 2009 to July 2010 by extensive surveying in the rapids and waterfalls inside and outside of national parks wildlife sanctuaries and protected areas. The samples collected are classified into 2 subfamilies which are Tristichoideae and Podostemoideae. The former contains 2 genera and 3 species Dalzellia kailarsenii Terniopsis sp. 1 Terniopsis sp. 2. The latter has 4 genera and 9 species Hanseniella heterophylla Hydrobryum japonicum Hydrobryum loeicum Hydrobryum tardhuangense Hydrobryum vientianense Hydrobryum sp. 1 Hydrobryum sp. 2 Polypleurum sessile Thawatchaia trilobata. The highest number of species occurs in Hydrobryum with 6 species following by Terniopsis with 2 species. The other four genera have one species each. Based on morphological and molecular analyses revealed that 2 species of the genus Hydrobryum are new and 2 taxa of Terniopsis are also new species. Polypleurum sessile and Thawatchaia trilobata are new recorded in Loei province. The result from this study indicates that the genus richness is relatively high in Loei province which encompasses 60% of the total number of genera (10) in Thailand. The plants in vegetative phase are completely submersed in swiftly running water during a warm wet season (May-October). The plants flower and set fruits and seeds when exposing to air during water level drop in a cool dry season (November- February).