Up until a few weeks ago I had thought this species below was holosericeoides, due to the nearly identical foliage. Maggie Hellis consulted Wisnu Ardi recently as to the accuracy of this ID however, and it turns out that it is more likely aketajawensis! This ID was primarily based on the male flowers having four tepals, as opposed to two in holosericeoides. It is strange, as the ovary my plant is green, not pink as shown for akajawensis. But, tepal count overrides ovary color as far as significant floristic traits go.
The paper describing all three species can be found here.
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.
And, some info on holosericeoides, because I already wrote it out before Maggie and Wisnu correctly identified it.
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.
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.