Recent explorations of Podostemaceae have discovered 2 new species to science (Dalzellia TWA-216 และ Hydrobryum TWA-198) from Phitsanulok Province and 3 more genera and six more species from previously known (2 genera and 4 species). Totally five genera and 10 species occur in Phitsanulok and Phetchabun provinces. Based on morphological and molecular evidence the taxa are classified into subfamily Tristichoideae including 2 genera and 3 species (Dalzellia 2 spp. and Terniopsis 1 sp.) and subfamily Podostemoideae consisting 3 genera and 7 species (Hanseniella 1 sp. Hydrobryum 5 spp. and Thawatchaia 1 sp.). The species found in both provinces are Hy. phetchabunense and Hy. tardhuangense while D. kailarsenii is found only in Phetchabun. The plants discovered only in Phitsanulok include Dalzellia TWA-216 Hydrobryum TWA-198 Han. heterophylla Hy. bifoliatum Hy. kaengsophense Th. trilobata and T. minor. Among the species found Hy. tardhuangense and Th. trilobata are also distributed to the Lao PDR and the rests are endemic to Thailand.

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.