Fig. 1: Two pieces of sediment specimens with the liverworts

The story of this mysterious herbaceous plant began on 26 June, when I found a large population of liverworts growing on semi-moist, hardened sediment in an open-air carpark. The sediment had likely accumulated on the concrete surface over a long period through rainwater runoff. I collected two sediment pieces with liverworts attached and placed them in one of my pots for observation (Fig. 1). The liverwort was later identified as Riccia treubiana, a species considered relatively common in Singapore according to the Singapore Flora Checklist (page 33). A newly released article [1] on a Singapore study related to this liverwort also appeared a few days ago. This is the second liverwort that I have added to my website; the first was Pallavicinia lyellii (Ribbonwort), which I spotted in 2017.

Fig. 2: Seedling of the unknown plant		Fig. 3: Flower of the unknown plant

On 25 July, I noticed a seedling (Fig. 2) growing near the edge of one collected specimen. At that early stage, it was difficult to determine its species. The young plant looked interesting, however, and had likely arrived on the sediment as a seed. To give it a better chance of surviving and eventually revealing its identity, I moved it to a small pot of its own. As it grew, I first suspected it might be a seedling of Cyanthillium cinereum (Little Ironweed), a very common wild herbaceous plant, because of its leaf characteristics.

Fig. 4: Whole plant

The first flower bud appeared on 4 August and bloomed on 7 August, revealing a plant I had not seen before. Its flower (Fig. 3) resembled that of Torenia crustacea (Brittle False Pimpernel). I checked the Singapore Flora Checklist for species in the family Linderniaceae, to which Torenia crustacea belongs, and compared the entries with images on iNaturalist. None appeared to match. I also searched species in the family Acanthaceae, but again found no promising lead.

On 10 August, I turned to the collective knowledge of the iNaturalist community by uploading several images to the website. As of today, there have been no comments or species suggestions.

Fig. 5: Fruit and seeds of the unknown plant

While I waited for clues from the community, the plant continued to grow. It is a low-lying plant with opposite leaves. The mature plant (Fig. 4) is relatively small, about 6 centimetres (cm) tall including the racemic inflorescence, which accounts for about 5 cm of that height. Each small flower stalk is attached along a single central stem, with the oldest flowers at the bottom. New flower buds develop upward and open last at the top. After blooming, each flower drops off on the second day. Two branches have emerged on opposite sides of the second leaf node, and more appear to be emerging from the base.

The fruit resembles a capsule about 1 millimetre in diameter. On 20 August, the first fruit split slightly at the top, with the green sepals still attached at the base. After carefully prying open the top, I saw many tiny seeds fall out. They were light brown, slightly elongated, and tapered at one end (Fig. 5). The seeds reminded me of those I had seen in Mecardonia procumbens (Yellow-flowered Waterhyssop), a member of the family Plantaginaceae that I investigated in February 2025. I therefore checked other species in this family as well, but nothing promising emerged.

Even with all these plant features now available, I still have no clue about its identity. Although I did not succeed in identifying the plant, the effort helped me spot past identification errors in two other plants: Blechum pyramidatum and Strobilanthes glaucescens. These should instead be Hemigraphis sumatrensis and Strobilanthes schomburgkii, respectively.

Reference:

[1] Chen XY, Ho BC. Human-mediated vegetative dispersal of the liverwort Riccia treubiana in a tropical city. Urban Ecosystems 2026;29:238. | Read article |