This month, I saw a long-missed small herbaceous plant that sprout in my pot. This plant did appear in my pot from time to time but it is relatively rare, even in the wild. Before this note, I had identified it as Cardamine hirsute (Hairy Bittercress). This had changed to Cardamine occulta (Nursery Bittercress) after I penned this short note.

According to botanical description from the Flora of North America website, the stem of Cardamine hirsute is unbranched or branched at the base of the plant. This description did not fit well with the Cardamine species in my pot which had branched stems above the base as well. Then I saw a statement in the same page that indicated that “Herbarium specimens of Cardamine hirsuta have been misidentified as C. oligosperma". Interestingly, the images of Cardamine oligosperma found online appeared to match well with the specimen in my pot.

Another Cardamine species that came close to the appearance of the one that I had was Cardamine flexuousa (Wavy Bittercress). However, this species should have a rosette leaf arrangement at the base of the plant which was not the case for the plant in my pot. A good comparison including pictures between Cardamine hirsute and Cardamine flexuousa is available at the Botanical Society of Scotland blog.

In a checklist titled “The Names Used for Singapore Plants Since 1900” published in 1993 [1], Cardamine flexuousa was listed in item number 635 under the family Cruciferae (the older family name of Brassicaceae). More recently, in the checklist of macrophytes (aquatic plants growing in or near water) in Singapore published in 2022 [2], Cardamine flexuousa was listed as well. Nevertheless, I doubt my plant was Cardamine flexuousa since there is no rosette leaf arrangement at the base of the plant. Nothing on Cardamine hirsute was found in any local publications in my online search.

The most common Cardamine species talked about online in Singapore is Cardamine lyrate (Chinese Ivy), an imported plant used in the aquarium. Looking up on the records of Cardamine species available in Singapore in the iNaturalist website on 23 July, Cardamine hirsute had 6 observations. The outlier was a single observation on Cardamine occulta uploaded this month. I did a check on the image of this species from other sources [3, 4], and it seems to match well with the appearance of my plant as well.

With the searches done, it was down to Cardamine oligosperma or Cardamine occulta. The distribution of Cardamine oligosperma is limited to the Canada, U.S.A. and Mexico regions according to the Plants of the World Online website. On the other hand, Cardamine occulta is found in Tropical Asia as indicated in the same website. Also, an article from the PhytoKeys journal published in 2016 had clarified the naming of this Asian plant as Cardamine occulta versus Cardamine flexuousa [5]. With that, I had decided to adopt Cardamine occulta as the botanical name of the plant seen in my pot.

References:

[1] Turner IM. The Names Used for Singapore Plants Since 1900. Gard Bull Sing 1993;45(1):1-287. | Read article |

[2] Sim DZH, Mowe MAD, Chong KY, Yeo DCJ. An overview and checklist of non-native and cryptogenic vascular macrophytes in Singapore’s fresh waters. Nature in Singapore 2022;Supplement 1:190-206. | Read article |

[3] Pliszko A. First record of Asian Cardamine occulta Hornem. (Brassicaceae) in Poland. BioInvasions Records 2020;9(3):655-659. | Read article |

[4] Hruševar D, Mesaroš J, Vladović D, Vucić A, Belamarić I, Surać L, Mitić B. Cardamine occulta Hornem. – a new concealed alien plant in the flora of Croatia. Natura Croatica 2021;30(1):207-215. | Read article |

[5] Marhold K, Šlenker M, Kudoh H, Zozomová-Lihová J. Cardamine occulta, the correct species name for invasive Asian plants previously classified as C. flexuosa, and its occurrence in Europe. PhytoKeys 2016;62:57-72. | Read article |