Micranthemum micranthemoides (syn. Hemianthus micranthemoides),[1] commonly known as Nuttall’s mudflower or pearlweed in aquascaping,[2] [3] is an extinct species of subaquatic Micranthemum that previously inhabited wet areas from Virginia to New York. It is commonly misidentified as a similar species, Micranthemum glomeratum, in aquascaping.[4]
Micranthemum micranthemoides was a small subaquatic glabrous annual that exhibited creeping stems and ascending branches. Micranthemum micranthemoides grew 5-20 cm in height. Micranthemum micranthemoides had opposite, elliptic leaves measuring 2–5 mm. Leaves were entire. Flowers were both solitary and axillary. Each flower's collora was white and measured 2 mm. Flowers contained two stamens, which were inserted around the collora's throat. Micranthemum micranthemoides flowered from September to October.[5] It's seeds were oblong to narrowly obconic.[6]
Micranthemum micranthemoides previously occurred in the mid-atlantic region of the United States. It grew in wet areas from Virginia to New York.[4] Before its extinction, it was a rare occurrence in tidal mudflats[5] and in the intertidal zone of river estuaries. It is said to have been highly specialized to these habitats.[7] Micranthemum micranthemoides grew in sandy and gravelly substrates. It was last seen on 13 September 1941 by Fernald & Long.[8]
Plants labeled Micranthemum micranthemoides or Hemianthus micranthemoides are commonly sold in aquascaping as "pearlweed", but are not truly of this species. When examined, these plants sold as pearlweed were actually of a similar species, Micranthemum glomeratum, which is native to Florida. This misidentification was confirmed by Emeritus Ernie Schuyler when the aquascaping plants were compared to herbarium speciemens and descriptions of Micranthemum micranthemoides.[4] Micranthemum micranthemoides probably has never been cultivated as an aquarium plant.[7]