The ornamental design for a plantholder, as shown and described.
FIG. 1 is an isometric view of a plant holder, shown in use;
FIG. 2 is a front elevation view thereof, the rear elevation, the left elevation, and the right elevation being mirror images thereof;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
The evenly spaced broken lines in FIGS. 1 and 3 are included to show articles in the environment and a portion of the plant holder that form no part of the claimed design.
The long and short broken lines in FIG. 2 indicate the appearance of any portion of the article between the break lines forms no part of the claimed design.