Abstract
A taxonomic revision of the native
Pinus
L. (Pinaceae) species in Thailand is presented. Two species,
P. kesiya
Royle ex Gordon and
P. latteri
Mason, are recognized and enumerated with updated morphological descriptions, photographs, and an identification key, together with notes on distribution, habitat and ecology, phenology, conservation status, etymology, vernacular names, uses, and specimens examined.
Pinus kesiya
is neotypified (second-step neotypification), and
P. kasya
Royle ex Parl., a synonym of
P. kesiya
, is lectotypified (second-step lectotypification).
Pinus kesiya
is assessed as Least Concern (LC), whereas
P. latteri
is assessed as Near Threatened (NT). Morphologically, the two species can be distinguished by bark fissuring pattern, thickness, and color; number of needles per fascicle; needle morphology (including rigidity, posture, and shape and diameter in transverse section); length/width ratio of seed cones when closed; apophysis shape and outline; seed scale thickness; relative length of seed wings; and presence or absence of a grass stage. The two species differ ecologically in elevational range and habitat preference, with
P. kesiya
occurring at higher, more humid montane sites and
P. latteri
at lower, drier habitats.
Pinus kesiya
and
P. latteri
differ in needle shape in transverse section, which is triangular in
P. kesiya
and semicircular in
P. latteri
. They also differ in resin duct number and position, with
P. kesiya
having 3–4 external resin ducts near the hypodermis, whereas
P. latteri
has 2–3 medial resin ducts between the endodermis and hypodermis. Pollen morphology is not diagnostic for species delimitation.