Begonia holosericeoides is endemic to the lowland forest of Halmahera Timur, Indonesia, and strongly resembles Begonia holosericea. “The specific epithet is a compound of holoserecia (the similar species) and -oides (in Greek compounds: resembling). It refers to the creeping habit and adaxial leaf pattersn, which are similar to the conditions found in B.holosericea.”
From the publication describing the species by Wisnu Ardi et al, holosericeoides is found “on vertical moist rock surfaces, including limestone substrates, in full shade, in primary rainforest at ca. 145 m asl.”
It is in the section Petermannia, a section known to many growers as having female flowers come out in advance of males (not always, but often). In most other Begonia sections, males will routinely come out before females, allowing for easy self-fertilization. With female flowers coming out first, there is the risk that the ovary drops before the males have had the opportunity to develop and open, limiting the likelihood of self-fertilization.
The flowers themselves are enormous for the size of the plant, as you can see from the photo with my thumb in it. The edges of the tepals are subtly pink.
Ardi, Wisnu & Kusuma, Yayan Wahyu C & Lewis, Carl & Risna, Rosniati & Wiriadinata, Harry & Abdo, Melissa & Thomas, Daniel. (2014). Studies on Begonia (Begoniaceae) of the Molucca Islands I: Two New Species from Halmahera, Indonesia, and an Updated Description of Begonia holosericea. Reinwardtia. 14. 19-26. 10.14203/reinwardtia.v14i1.391.