A novel case of autogamy and cleistogamy in Dendrobium wangliangii: A rare orchid distributed in the dry‐hot valley

Abstract

Dendrobium wangliangii is an epiphytic orchid distributed in the Jinshajiang dry‐hot valley in Luquan County, Yunnan Province, China. Most Dendrobium spp. typically have a low fruit set, but this orchid shows a higher fruit set under natural conditions despite the lack of effective pollinators. The pollination biology of the critically endangered D. wangliangii was investigated in this study. A fruit set rate of 33.33 ± 4.71% was observed after bagging treatment in 2017 and a high fruit set rate (65.72 ± 4.44% in 2011; 50.79 ± 5.44% in 2017) was observed under natural conditions, indicating that D. wangliangii is characterized by spontaneous self‐pollination. The anther cap blocked the growing pollinium; thus, the pollinium slid down and reached the stigmatic cavity, leading to autogamous self‐pollination. Specifically, 51.50% of 162 unopened flowers (total 257 flowers) of this Dendrobium species under extreme water‐deficit conditions developed into fruits, suggesting the presence of cleistogamy in D. wangliangii. Here, cleistogamy may represent the primary mode of pollination for this orchid. Spontaneous self‐pollination and specific cleistogamous autogamy could represent major adaptions to the drought and pollinator‐scarce habitat in the Jinshajiang dry‐hot valley.

Orchid Reintroduction Based on Seed Germination-Promoting Mycorrhizal Fungi Derived From Protocorms or Seedlings

“…Moreover, they are popular flagships for habitat conservation. However, orchids are currently among the most threatened flowering plants, with many species on the verge of extinction in the wild due to over-collection, loss of habitats, or climate change (Liu et al, 2015 ; Gale et al, 2018 ; Hinsley et al, 2018 ; Wang et al, 2019 ). Furthermore, most orchids require specialized habitats and are usually in small populations with a high dependence on pollinators, symbiotic germination fungi, and host trees for epiphytic species, further making them particularly vulnerable to extinction (Roberts and Dixon, 2008 ; Selosse, 2014 ; Fay et al, 2015 ; Rasmussen et al, 2015 ; Keppel et al, 2016 ; Fay, 2018 ; Gale et al, 2018 ).…”

Pollen biology and reproductive ecology of selected paleotropical Dendrobiums and its commercial hybrids

“…In contrast, those pollinators may quite be abundant in natural areas where indigenous species naturally exist. However, it is an accepted fact that orchids, particularly dendrobiums, have a low rate of pollinator visits (Wang et al 2019). Even though the floral morphology, colourfulness, flashy and comparatively large size tend to attract pollinators, the scarcity of specific pollinators in the native environment may be the cause for the absence of pollinator visitation of the imported hybrids.…”

“…Flowers that have easily accessible floral rewards with nectar or/and pollen exerted beyond the petals are unrestrictive. Flowers with a tube radius of at least 2 mm are considered as unrestrictive and less than 2 mm are considered restrictive (Wang et al 2019), (3) Flower colour variation in the different parts of the flower, (4) Number of flowers in the inflorescence that comprise the display signals for pollinator attraction, (5) Flower length (distance between the tip of the dorsal sepal to the tip of the labellum), (6) Floral width (distance between lateral sepals), (7) Column colour, (8) Labellum colour, (9) Labellum disk colour, (10) Presence or absence of scent (determined by smell), (11) Presence or absence of nectar at the base of the column (determined by observation of naked eye).…”

Chemical Composition of Essential Oil from Flowers of Five Fragrant Dendrobium (Orchidaceae)

“…Therefore, a defensive role for 2,4-di-tert-butylphenol in D. chrysanthum cannot be excluded. Finally, it is interesting to notice that among the Dendrobium and Densiflora sections, three self-incompatible species, D. amabile and D. harveyanum , and D. chrysanthum , respectively, showed a reduced spectrum of volatiles [ 51 , 52 ]. It is tempting to hypothesize that this has a role in pollination biology; indeed, discouraging pollinators from pollinating more flowers of the same plant and inducing pollinators to visit different individuals, would result in a higher fruit set.…”