A pocket-sized pictorial guide to Singapore’s wildflowers was published in 1985 [1], more than 40 years ago, and I once owned a copy. Years ago, I created a pictorial page featuring all 74 plant species in the booklet. On revisiting the list, I noticed that one species, Thunbergia alata (Black-eyed Susan Vine), no longer appears to exist in the wild in Singapore.

When I was a child living in an eastern kampong in the 1970s, this climber was very common. I remember it clearly for its distinctive bright-yellow flower with a black centre. Since starting this website in 2007, I have seen the climber only twice: in September 2008 near the former ORTO leisure park in Yishun, and in May 2013 at a park near my home. The Yishun plant (Fig. 1) appeared to be growing wild on a wire fence, but the entire area has since been cleared for a new housing development. The park specimen (Fig. 2) was cultivated by NParks, but it fared poorly and disappeared within a few months.

Fig. 1: Thunbergia alata spotted in Yishun area in 2008.		Fig. 2: Thunbergia alata spotted in a park in 2013.

The 2022 Singapore flora checklist lists Thunbergia alata as a non-native naturalised species (page 122). As viewed on 27 September, iNaturalist had more than 20,000 observations of this climber worldwide, but none from Singapore; neighbouring Malaysia had 41 observations. I also found a University of Hawaii at Manoa article titled “The Mysterious Disappearance of a Weedy Vine (Thunbergia alata) from O'ahu: Testing Possible Roles of Competition from New Invaders and an Altered Disturbance Regime.” Although I could not access the full article, its abstract appears to describe a disappearance similar to that of the plant in Singapore.

To identify other changes affecting the species listed in the 1985 booklet, I compiled iNaturalist information for all 74 species. In addition to the status of Thunbergia alata noted above, the tabulated results revealed two other noteworthy findings.

Fig. 3: Asystasia intrusa (African Coromandel) photographed this week in a park next to my home.

The first finding concerns a change in the accepted botanical name of the very common herbaceous plant Asystasia gangetica subsp. micrantha (Fig. 3). Rather than being treated as a subspecies of Asystasia gangetica (Chinese Violet), it is now recognised at species level as Asystasia intrusa (African Coromandel) by iNaturalist and Plants of the World Online. The name change appears to have occurred between 2022 and 2023, which may explain why many websites still use the former name. Some, including the Flora of Zimbabwe, have already adopted the update. I have updated my website accordingly.

The second finding concerns Smut Grass (Sporobolus indicus). Although this grass is common throughout Singapore, including urban areas, iNaturalist had no observations from the country. Further research showed that the situation is more complex than it first appeared.

The Singapore flora checklist lists three Sporobolus species (page 631): Sporobolus indicus, Sporobolus tenuissimus, and Sporobolus virginicus, the last of which is considered nationally extinct. It also recognises two varieties of Sporobolus indicus: var. flaccidus and var. major. However, Sporobolus indicus var. major is now treated as a synonym of Sporobolus fertilis, while Sporobolus indicus var. flaccidus is a synonym of Sporobolus diandrus. This brings the apparent total from three Sporobolus species to five. These changes are likely recent, as they were not reflected in the 2022 Singapore flora checklist.

Fig. 4: Specimen of Sporobolus species collected came with a young inflorescence.

iNaturalist records four Sporobolus species in Singapore: Sporobolus diandrus, Sporobolus fertilis, Sporobolus tenuissimus, and Sporobolus pyramidalis. After accounting for the botanical name changes noted above, the first three align well with the Singapore flora checklist. Sporobolus pyramidalis is an addition not included in that checklist.

The images on my website currently labelled Sporobolus indicus may include both Sporobolus diandrus and Sporobolus pyramidalis. Plants identified as Sporobolus indicus are readily found in the open-air car park beside my apartment block. To investigate further, I collected a specimen with a young inflorescence this week (Fig. 4) and placed it in a pot. I will update the species image page once I have obtained more photographs of the plant.

Reference:

[1] Foo, T.S. 1985. A Guide to the Wildflowers of Singapore. Singapore: Singapore Science Centre.