Placidium arboreum is a crustose lichen that grows on trees, particularly oak and cedar, in East and Central Texas. It has a gray to white thallus with a rough, wart-like surface and black apothecia. The species is commonly found in shaded areas with high humidity, such as along streams and in woodland edges. In Texas, it typically occurs on the trunks and branches of mature trees, often in association with other lichens and mosses.
Tree stipplescale lichen Placidium arboreum on a large winged elm near a creek, on mossy side opposite to the creek near Lone Star Hiking Trail near Pole Creek in Sam Houston National Forest. Richards, Texas, March 1, 2019 Lone Star Hiking Trail, Montgomery, TX 77356, USA
Rounded green lobes of tree stipplescale lichen (Placidium arboreum) on a large winged elm near a creek, on mossy side opposite to the creek near Lone Star Hiking Trail near Pole Creek in Sam Houston National Forest. Richards, Texas, March 1, 2019 Lone Star Hiking Trail, Montgomery, TX 77356, USA
Green lobes of tree stipplescale lichen (Placidium arboreum) on a large fallen oak on Lone Star Hiking Trail near Pole Creek in Sam Houston National Forest. Richards, Texas, December 12, 2020 Lone Star Hiking Trail, Montgomery County, Texas, United States
Tree stipplescale lichen (Placidium arboreum) with green mosses on a large fallen oak on Lone Star Hiking Trail near Pole Creek in Sam Houston National Forest. Richards, Texas, December 12, 2020 Lone Star Hiking Trail, Montgomery County, Texas, United States
Tree stipplescale lichen (Placidium arboreum) on a fallen oak near Pole Creek on North Wilderness Trail of Little Lake Creek Wilderness in Sam Houston National Forest north from Montgomery. Texas, December 15, 2021 Lone Star Hiking Trail, Montgomery County, Texas, United States
AI-generated summary of observations
Observations of Placidium arboreum in East and Central Texas reveal its presence on various tree species, including winged elm and oak. The lichen was found growing on mossy sides of trees, often near creeks, such as Pole Creek in Sam Houston National Forest. In Richards, Texas, it was observed on a large winged elm near Lone Star Hiking Trail, with rounded green lobes. On fallen oaks, the lichen was seen growing alongside green mosses, as noted on December 12, 2020, and again on December 15, 2021, in Little Lake Creek Wilderness. The species appears to thrive in shaded, moist environments, with multiple sightings in the same general area over a two-year period. Its growth patterns and associations with other organisms, like mosses, were consistent across observations.