Micranthemum micranthemoides

Micranthemum micranthemoides (syn. Hemianthus micranthemoides),^[2] commonly known as Nuttall's mudflower or pearlweed in aquascaping,^[3][4] is an extinct species of subaquatic Micranthemum that previously inhabited wet areas from Virginia to New York.^[5] It is commonly misidentified as a similar species, Micranthemum glomeratum, in aquascaping.^[6]

Micranthemum micranthemoides
Conservation status
Possibly Extinct  (NatureServe)[1]
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Lamiales
Family:	Linderniaceae
Genus:	Micranthemum
Species:	M. micranthemoides
Binomial name
Micranthemum micranthemoides Wettst.
Synonyms[2]
Synonymy Globifera micranthemoides Kuntze Hemianthus micranthemoides Nutt. Hemianthus micranthus (Pursh) Pennell Micranthemum micrantha (Pursh) Alph.Wood Micranthemum nuttallii A.Gray Herpestis micrantha Pursh Herpestis micrantha Elliott

Description

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] Its seeds were oblong to narrowly obconic.^[7]

Distribution and habitat

Micranthemum micranthemoides previously occurred in the mid-atlantic region of the United States. It grew in wet areas from Virginia to New York.^[6] 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.^[8] Micranthemum micranthemoides grew in sandy and gravelly substrates. It was last seen on 13 September 1941 by Fernald & Long.^[9]

Misidentification

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 Academy of Natural Sciences Botany Curator Emeritus Ernie Schuyler when the aquascaping plants were compared to herbarium specimens and descriptions of Micranthemum micranthemoides.^[6] Micranthemum micranthemoides probably has never been cultivated as an aquarium plant.^[8]