Trees On Stamps :

Here is Guatemala's 1963 4c airmail stamp (Sc #C273) depicting a Ceiba, or kapok tree (Ceiba pentandra) which in 1955 had been declared the country's national tree.

From wikipedia, "The Ceiba, or ya'axche' (in the Mopan Mayan language), symbolized to the Mayan civilization an 'axis mundi' which connects the planes of the underworld (Xibalba) and the sky with that of the terrestrial world."

The 50 centavos value (Sc #581) from El Salvador's 1938-9 pictorial definitive series shows a maquilishuat tree in bloom.

From wikipedia, "Tabebuia rosa, also called pink poui, and rosy trumpet tree is a neotropical tree that grows up to 30 m (98 ft) and can reach a diameter at breast height of up to 100 cm (3 ft). It is the national tree of El Salvador, where it is called Maquilishuat."

On August 1, 1995 Japan issued this 50 yen stamp (Sc #Z166) depicting a line of Japanese elm trees (Zelkova serrata), also known as keyakis or Zelkovas for Miyagi prefecture.

Photograph from wikipedia shows Noma Keyaki. They say, "Noma Keyaki, a 1000-year old Zelkova in Nose near Osaka in Japan, 25 meters tall, 11.95 meter trunk circumference; second-largest known specimen."

This se-tenant pair of 12c stamps (Sc #734a) was issued by Canada on May 26, 1977 to commemorate the birth centenary of Canadian artist and outdoorsman Thomas John Thomson (1877-1917). The stamps were printed together in a traditional sheet in "checkerboard" fashion, so that horizontal and vertical se-tenant pairs were produced.

The stamps show two of Thomson's oil on canvas landscapes. On the left is Autumn Birches (1915), and on the right is April in Algonquin Park (1917). The artist died at age 40 (1917) in a canoeing accident in Algonquin Park.

Here is the 20 yen value (Sc #433) from Japan's 1948-9 Industry definitive series. Stamp depicts forestation/tree planting.

On January 24, 2021 the USA issued this 7.95 dollar value (Sc #5554) as a part of its American Landmarks expedited service rate series of pictorial definitive stamps. Stamp depicts the sabal, or cabbage palms (Sabal palmetto) outside of Saint Augustine Florida's Castillo de San Marcos (1672). The Castillo was "Built by the Spanish to defend Florida and the Atlantic trade route...(it) preserves the oldest masonry fortification in the continental United States" (U.S.National Parks Service).

Regarding the trees, wikipedia says, "Sabal is a genus of palms endemic to the New World. Currently, there are 17 recognized species of Sabal, including one hybrid species."

Colombia
National Natural Parks
July 19, 2022
Booklet of ten, one stamp depicts Árbol polvillo (Handroanthus serratifolius).

French Polynesia
Palm Tree Species of Polynesia
April 9, 2021
The stamp set depicts Pelagodoxa henryana and Pritchardia mitiaroana.

Fiji 1994 SINGPEX minisheet
The stamp set depicts Neoveitchia storckii, a species of palm tree endemic to the island of Viti Levu in the Fiji Islands.

African trees and shrubs, designed by the Belgian artist Jean Van Noten and issued by Rwanda on August 27, 1979:

Polyscias fulva
Entandrophragma excelsum
IIlex mitis
Kigelia africana
Ficus thonningi
Acacia senegal
Symphonia globulifera
Acacia sieberana

Estonia
Estonian Forest Trees
2022: Curvy Birch (Betula pendula var. carelica
2023: European spruce (Picea abies)

Malawi
Trees and Plants
October 9, 2016
Set of 12, one stamp depicts neem tree known for its health benefits.

United States
Winter Scenes
October 16, 2020
Set of ten, one stamp entitled Evergreens depicts pine trees from Vermont.

Bangladesh
Japan World Stamp Exhibition
July 21, 2011
Set of six, one stamp depicts a cherry tree in full bloom.

Hungary
Our Natural Assets
August 5, 2020
The stamp depicts Tatar maple (Acer tataricum).