Online Resources: | Flora of North America | iNaturalist |

I had previously named this naturalised plant as Acalypha alopecuroidea (Foxtail Copperleaf). In November 2021, I had switched it to the current name, Acalypha arvensis, which I believe should be the correct name of this plant based on a local publication in 2020.

In the iNaturalist website viewed on 21 November 2021, there were 2 sightings of Acalypha arvensis in Singapore --- both recorded in 2021. On the other hand, there were 9 sightings for Acalypha alopecuroidea in Singapore from the same website between 2017 and 2021. All of them might be Acalypha arvensis.

In the NParks Flora & Fauna Web, the name Acalypha aristata was used instead and it listed Acalypha arvensis as a synonym which is in line with the accepted name indicated in the World Flora Online website. The same treatment of the names was also reported in a 2009 publication from Taiwan [2]. However, the Flora of North America website stated that "Some recent literature misapplies A. aristata Kunth to this species, but that name is a synonym of A. alopecuroidea".

According to the Flora of North America website, the stem of Acalypha alopecuroidea is described as "stipitate-glandular" which means having hairs with a rounded gland at the distal end, also known as glandular trichomes. The same description on this feature was also found in a 2012 publication in PhytoKeys journal [3].

Reference:

[1] van Welzen PC, Middleton DJ, Lindsay S. Flora of Singapore precursors, 21: New records of Euphorbiaceae for Singapore. Gardens' Bulletin Singapore 2020;72(2):143-158. | Read article |

[2] Chen SH, Su JY, Wu MJ. Notes on Two Newly Naturalized Plants in Taiwan: Evolvulus nummularius (L.) L. (Convolvulaceae) and Acalypha aristata Kunth (Euphorbiaceae). Taiwania 2009;54(3):273-278. | Read article |

[3] Sanz JM, Rodríguez PM. Synopsis of Acalypha (Euphorbiaceae) of continental Ecuador. PhytoKeys 2012;(17):1-17. | Read article |

The one in my pot did not have stipitate gland on the stem. The long slender catkin-like structure contains packed male flowers. The broader greenish catkin-like structure contains the female flowers and eventually housed the fruits. Stipitate glands can be found on the modified leaf structure (bracts) that housed the female flowers.

Close-up views: