Abstract
Argyreia siamensis is extremely rare, and very little is known about its reproduction. The species has colorful flowers that seem likely to attract pollinators, but population sizes are typically small (<30 individuals). To determine whether poor reproduction contributes to its rarity, we investigated its mating system and potential pollinators in two populations. We also examined the staminal trichomes and floral nectary to investigate their role in pollinator attraction. The mating system was assessed with a bagging experiment and pollinator visits were recorded with action cameras. Additionally, we tested the staminal trichomes and floral nectary for terpenes and flavonoids and examined floral nectary micromorphology via scanning electron microscope and compound light microscope. Our results reveal that A. siamensis is self-incompatible and dependent on pollinators; the western population was pollinated by bees (Meliponini and Amegilla), while the eastern population was mainly pollinated by skipper butterflies (Hesperiidae). Both staminal trichomes and the floral nectary appear to contribute to pollinator attraction through the presence of terpenes and flavonoids (in both secretory structures) and nectariferous tissue and nectarostomata (in the nectary). Our results indicate that A. siamensis has reliable and effective pollinators and that insufficient pollination is likely not a primary cause of its rarity.
Highlights
Tropical regions are important biodiversity hotspots [1,2], yet they are the regions where we are still missing the most information [3]
Argyreia siamensis is a rare plant species endemic to Thailand, but little is known about the species, and why it is rare
Our findings reveal that A. siamensis is self-incompatible and dependent on pollinators
Summary
Tropical regions are important biodiversity hotspots [1,2], yet they are the regions where we are still missing the most information [3]. Numerous studies have cautioned that Data Deficient taxa are often classified as such because they are not common, which means that many of them may be threatened [4,5,6,7] One such species with a small geographic range, few known populations, and only limited information is Argyreia siamensis (Craib) Staples (Convolvulaceae), a rare morning glory species that is endemic to Thailand [8,9]. Flowering occurs from July to November, and fertilized flowers develop into brown berries with red sepals [10] This species was originally known to occur only in the northern and western parts of Thailand, a population was recently discovered in an eastern province.
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