I was particularly intrigued by buttonweeds, primarily because I aimed to understand the complex identity of the plants within this group. Buttonweeds are commonly found along roadsides, in parks, and in wild areas of Singapore. Due to their lack of commercial or horticultural value, they have not been extensively studied or documented, although some varieties are regarded as medicinal herbs [1-5]. Buttonweeds are distinguished by their button-like inflorescences, which can be found at the tips of spreading branches or around leaf nodes. These small to tiny flowers are typically white.

Buttonweed is a common name for similar-looking plants. Although different species of buttonweeds may appear alike and belong to the same plant family (Rubiaceae), they are not classified within the same genus. The flowers of these plants are typically very small, making their features challenging to observe clearly with the naked eye. Consequently, I encountered difficulties in distinguishing the various species of buttonweeds, which led to frequent changes in the labelling of their images on my website. While many pictures of buttonweeds are available online, it can be challenging to verify their correct identification due to conflicting images. Additionally, few publications provide photographs of the buttonweeds mentioned. Therefore, the botanical names used for the images on my website are based on my own deductions.

The goal of this brief document is to present sampled pictures of buttonweeds found in Singapore, displaying 2 photos of each species for a quick visual comparison. Links are included to access the full image deck of each species. Buttonweed species that do not possess the characteristic button-like inflorescences, such as Spermacoce latifolia (Broad leaved buttonweed), have been omitted.

Mitracarpus hirtus (White Eye, Tropical Girdlepod):

DSC07388 (10)

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It appears that another species of buttonweed, Spermacoce parviceps, closely resembles Mitracarpus hirtus. According to the 2022 Singapore flora checklist, Spermacoce parviceps was considered extinct in Singapore. However, an observation of this species was reported on the iNaturalist website in June 2024.

Spermacoce exilis (Toothed Buttonweed, Pacific False Buttonweed):

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Spermacoce exilis closely resembles Mitracarpus hirtus in overall appearance, as both species exhibit an erect and branching growth habit with button-like inflorescences positioned similarly on the plants. The primary distinguishing feature is the presence of fine hairs on the leaf surfaces of Mitracarpus hirtus.

Spermacoce remota (Purple-leaved Buttonweed, Woodland False Buttonweed):

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Some leaves of Spermacoce remota exhibit light purple colouring around the edges.

Spermacoce ocymifolia (Slender Buttonweed):

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Spermacoce ocymifolia closely resembles Spermacoce remota. The leaves of Spermacoce ocymifolia lack the purple shades along the leaf margins. Furthermore, the mature plant of Spermacoce ocymifolia is the tallest among the buttonweeds discussed on this page.

Exallage auricularia (Eared Starviolet):

P6100370 (17)

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Exallage auricularia and Spermacoce ocymifolia share similar plant appearances. The distinguishing feature is the size of their white flowers, with Exallage auricularia having much smaller flowers. According to the 2022 Singapore flora checklist, the accepted botanical name is Hedyotis auricularia. I had adhered to the convention employed by the Plants of the World Online website, which considers Hedyotis auricularia as a synonym of Exallage auricularia.

Spermacoce verticillata (Shrubby False Buttonweed):

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Spermacoce verticillata has the narrowest leaves among the buttonweed species found in Singapore. It is commonly located in waterlogged wastelands or coastal regions.

Richardia scabra (Rough Mexican Clover, Florida Pusley):

PB300095 (24)

PB300080 (24)

Richardia scabra has a low, spreading growth habit.

References:

[1] Fan S, Weng W, Ji S. Pharmacognostic studies on three species of Spermacoce. J Holistic Integrative Pharmacy 2024;5(1):2-9. | Read article |

[2] Ekalu A. Medicinal uses, phytochemistry, and pharmacological activities of Mitracarpus species (Rubiaceae): A review. Scientific African 2021;11:e00692. | Read article |

[3] Ankad GM, Konakeri RT, Hegde HV, Roy S. Variation in pharmacognostic characters and polyphenolic contents among four species of medicinal plants from the genus Spermacoce (Rubiaceae). Indian J Pharm Sci 2015;77(4):446-452. | Read article |

[4] Sukart MA, Utamt R, Neoh BK, Ee GCL, Jusoh S, Nor SMM, Rahmant M. Antileukemic properties of Spermacoce species. Asian J Chemistry 2013;25(8):4595-4598. | Read article |

[5] Conserva LM, Ferreira JC Jr. Borreria and Spermacoce species (Rubiaceae): A review of their ethnomedicinal properties, chemical constituents, and biological activities. Pharmacogn Rev 2012;6(11):46-55. | Read article |

Last updated: January 2025