Trustees must be appointed in accordance with any conditions imposed by the trust instrument. A Trustee that has not been appoined to the office of trustee in accordance with the requirements of the trust instrument or statutory law is known as a Trustee de son tort (ie a Trustee of his own wrong).
A Trustee de son tort retains the liabilities of a lawfully appointed Trustee, but is unable to exercise the powers of a lawfully appointed trustee.
A transcript of Meier v Dorzan Pty Limited & Anor  NSWSC 664 can be found here.The case of Meier v Dorzan Pty Limited involved a superannuation fund and the Trust Deed made on 9 February 1996 required that the “Trustee of the Fund must be a constitutional corporation”.
A purported deed of variation and appointment dated 31 March 2000 purported to replace the corporate trustee with a natural person trustee.
Slattery J held the appointment to be invalid and the purported trustee to be a Trustee de son tort.
This case cited Jasmine Trustees Limited and Ors v Wells and Hind & Anor  3 WLR 810,  Ch 194,  EWHC 38 (Ch),  1 All ER 1142. A transcript of this case can be found here.
In this case Mann J states at :
“The effect of my conclusion in relation to issue (b)(i) is that the trustees who purported to appoint the trust property were themselves invalidly appointed. They acted in the trust, and became trustees de son tort, but nevertheless were invalidly appointed. As such trustees, they might be liable for breach of trust in the same manner as a trustee validly appointed, but that is a question of liability, not powers. That was the position in Pearce v Pearce  EngR 374;  22 Beav 248, 52 ER 1103.
Mann J continues at :
The Trustees” is defined as the originally appointed trustees and was to “include the trustees or trustee for the time being hereof”. It is clear to me that that means trustees properly appointed. Anyone improperly appointed is not appointed at all, and I fail to see how such a person can claim to exercise powers given to trustees under the deed.