Fatoua pilosa
[Mulberry Weed, Hairy Crabweed]

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Close-up views:

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The small herbaceous herb can be propagated by stem cutting. Simply cut a matured branch and stick it in the soil. The seed is about 1 millimetre (mm) in diameter with undulating surfaces. When the cymose flower head matured, the light brown tiny seeds can be seen half hidden on the top of the flower head. They were dispersed via an explosive mechanism. The seed was described as achene (dry fruit), reddish brown, compressed, 3-angled and about 1 mm by the Flora of China website.

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This small low-lying herb was discovered at an outdoor carpark lots next to my home in June 2015. It was not listed in the Singapore Flora checklist published in 2009. As there were tree-planting activities going on in the area, the seeds of this herb probably came along with the soil that were used to plant the trees.

Some reports such as the Prosea website have merged Fatoua pilosa and Fatoua villosa as the same plant. However, others such as the Plant List website and the Flora of China website has treated the 2 names as different species. More information on the complexity of this genus is available at the website by Arthur Lee.

Based on the description in the Flora of China website, the leaf of Fatoua pilosa is "not decurrent on petiole" while that of Fatoua villosa is "decurrent on petiole". Decurrent means that the leaf blades partly wrap or have wings around the petiole. It is quite clear that the leaves of the herb I saw were not decurrent on petiole.

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The table below compared some features of the two closely related plant based on the information from the Flora of China website.

Feature
Fatoua pilosa
Fatoua villosa
Chinese name
细齿水蛇麻
水蛇麻
Height
Up to 60 cm
30-80 cm
Stem
Branched
Erect, few branched or unbranched
Leaf blade
Triangular-ovate, 2.5-7.5 × 0.8-4 cm
Ovate to broadly ovate, 5-10 × 3-5 cm
Leaf base
Truncate to ± cordate and not decurrent on petiole
Cordate to truncate and decurrent on petiole
Leaf apex
Acuminate to acute
Acute
Inflorescences
Cymose
Cymose
Distribution
Taiwan, Indonesia, New Guinea, Philippines, Pacific Islands (New Caledonia)
China, Taiwan, Indonesia, Japan, Korea, Malaysia, New Guinea, Philippines; Australia