# Chromosome Number and Genome Size Evolution in _Brasolia_ and _Sobralia_ (Sobralieaee, Orchidaceae)
## 2 Results
### Chromosome Number and Genome Size Varies in Sobralieae
altissima_ with the largest genome size, the second group formed by _B. cattleya-B. dichotomous-B. flaza_, the third composed by _B. hirtzii_, and the last group formed by _B. portillae_ with the smallest genome size found in the genus (Figure 5a). The two _Elleanthus_ species differ two-fold in their genome size, which enabled the identification of those two species based on the genome size (F = 5.622, \(p\) < 2 \(\times\) 10\({}^{-16}\); Table 1). Among the 12 _Sobralia_ species, the estimated 1C-value presented a significant difference among species (F = 650, \(p\) < 2 \(\times\) 10\({}^{-16}\); Figure 5b), ranging from 1C = 3.43 pg in _S. fragrans_ to 1C = 8.05 pg in _S. luerorum_ (Table 1; Figure 5b). The three larger genome sizes were found in _S. luerorum_, _S. macrantha_, and _S. rosea_, while the two smaller ones were found in _S. crocea_ and _S. fragrans_, while the remaining species formed a heterogeneous group without clear differentiation among species (Figure 5b). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Species [n. FCM** & **Chromosome** & **Figure/** & **1C DNA Content** & **CV Sample** & **Genome Size** \\  & **S Specimens** & **Number** & **Reference** & **pg \(\pm\) SD** & **Mbp** & **\%** & **Category** \\ \hline \multicolumn{6}{c}{**Sect. _Intermediate_**} \\ \hline
20 & _S. crocea_[2] & 44 & Figure 4j & 3.77 \(\pm\) & 3695 & 5.00 & intermediate \\
21 & _S. fragrans_[1] & 42 & Figure 4k & 3.43 \(\pm\) & 3355 & 4.52 & small \\ \hline \multicolumn{6}{c}{**Sect. _Racenose_**} \\ \hline
22 & _S. gloriosa_ & 48 & Figure 4l & - & - & - & - \\
23 & _S. luerorum_[2] & 48 & Figure 4m & 8.05 \(\pm\) & 7872 & 4.14 & intermediate \\
24 & _S. rosea_[1] & 48 & Figure 4n & 5.93 \(\pm\) & 0.006 & 5800 & 3.48 & intermediate \\ \hline \multicolumn{6}{c}{**Complex _undatocarinata_**} \\ \hline
25 & _S. undatocarinata_[1] & - & - & 4.17 \(\pm\) & 4074 & 4.45 & intermediate \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
Figure 5: _Brasolia_ (**a**) and _Sobralia_ (**b**) genome sizes (1C-value). The 1C-value indicated by the same letter are not significantly different at _p_\(\leq\) 0.05 according to the [PERSON]’s multiple range test. Ancestral Reconstruction of Chromosome Number and Genome Size Indicate x = 25 and Small Genome Size for the Common Ancestor of Brasolia-Ellenanthus-Sobralia  
Regarding the ancestral reconstruction for chromosome number, for both trees, the ChromEvol suggested the same model as the best one: constant rate without duplication (Table 2). However, considering the \(\Delta\)AIC < 2, no differences were found among constant rate, constant rate with demi-polylploidy and the best model for ML and BI phylogenies (Table 2). The Model Adequacy test confirmed the null model, constant rate without polyploidy, as the most adequate considering the variance and entropy tests (\(p\) = 0.13 and 0.21 for ML and \(p\) = 0.31 and 0.35 for IB, respectively) but not the parsimony (\(p\) = 0.00 for both ML and BI), suggesting that the chromosome number transitions are variable among clades. The best models highlight the importance of dysploidy variation as the main mechanism in chromosome evolution in _Brasolia_, _Ellenanthus_ and _Sobralia_. The best model applied in both phylogenetic trees revealed similar results for most phylogenetic nodes. The base chromosome number x = 24 was suggested for the tribe Sobralieae, as well as for the genera _Brasolia_ and _Sobralia_, while x = 25 was suggested for genus _Ellenanthus_ (Figure 2). The descending dysploidy was more frequently detected than ascending dysploidy, while no duplication was observed (Table S2). Successive descending dysploidies were observed in both phylogenetic trees reaching x = 23 in the large group comprehending _S. atropubescens_, _S. sessilis_, _S. yuaperyensis_, _S. decora_, _S. fimbrita_, _S. powellii_ in IB phylogeny, but also grouping _S. bimaculata_, _S. vallecauana_, _S. crocea_, and _S. fragrans_ in ML phylogeny (Figure 2).