diff --git a/bin/ps/ps.1 b/bin/ps/ps.1
--- a/bin/ps/ps.1
+++ b/bin/ps/ps.1
@@ -29,7 +29,7 @@
 .\"     @(#)ps.1	8.3 (Berkeley) 4/18/94
 .\" $FreeBSD$
 .\"
-.Dd April 25, 2023
+.Dd June 18, 2023
 .Dt PS 1
 .Os
 .Sh NAME
@@ -226,6 +226,11 @@
 If all keywords have empty header texts, no header line is written.
 .It Fl p
 Display information about processes which match the specified process IDs.
+It implies the use of
+.Fl x .
+When combined with
+.Fl d ,
+all descendent processes are included.
 .It Fl r
 Sort by current CPU usage, instead of the combination of controlling
 terminal and process ID.