Abstract
ABSTRACT
Plastome evolution and biogeographic history remain poorly understood in mycoheterotrophic lineages. Here, we sequenced and assembled the complete plastome of
Monotropa callistoma
(Ericaceae), a fully mycoheterotrophic species, and compared it with other mycoheterotrophic plastomes. The
M. callistoma
plastome is 29,784 bp long, lacks the canonical quadripartite structure, and contains 40 genes, representing an intermediate level of reduction within Monotropoideae. Comparative analyses revealed extreme contraction in some lineages, including
Sciaphila
(12.8–21.5 kb), and a weak positive correlation between GC content and genome size. Within Monotropoideae, plastomes become smaller from the early‐branching
Pterospora
lineage to the more recently diverged
Monotropa
lineage. This reduction is accompanied by progressively poorer synteny and lineage‐specific loss of
rps23
in
Monotropa
. Phylogenomic analyses of 30 Ericaceae plastomes strongly supported Monotropoideae (bootstrap = 100) and clarified relationships among its 10 sampled genera. Divergence‐time estimation and ancestral‐range reconstruction placed the origin of Clade 1 (Pyroloideae, Arbutoideae and Monotropoideae) in Asia during the late Cretaceous to early Cenozoic. The lineage subsequently dispersed to North America via Beringia, whereas the
Monotropsis
+
Monotropastrum
+
Monotropa
clade later dispersed back to Asia during the late Eocene to early Oligocene. This history gave rise to East Asian endemics, including
Monotropa
humile and
M. callistoma
. These findings illuminate plastome reduction in mycoheterotrophs, resolve relationships within Monotropoideae, and support a complex history of bidirectional intercontinental dispersal.