An accomplished ecologist with 20+ years in the environment sector and over a decade of experience in leading for purpose organisations, Cassandra brings deep expertise in executive leadership, strategic planning, financial management, cross-sectorial partnerships and stakeholder engagement. She has a passion for driving behaviour change and promoting environmental stewardship and is excited to be uniting the collective voice of those dedicated to protecting plants—our planet’s life support system.
Board Members
Marianne Cullen
Chair
Marianne has 27 years of experience in government and consulting, including senior executive roles in the Federal Government and private sector. She has advised ministers, Cabinet, and boards on major policy reforms and led their implementation. Her expertise spans strategy, governance, stakeholder engagement, social license, and change management.
Awarded the Public Service Medal in 2013, she is also a Member of the Australian Institute of Company Directors.
With extensive skills in strategic planning, operations improvement, financial risk management and ITC System Transformation, Katherine is passionate about the growth of BGANZ and securing its long-term financial sustainability. Katherine holds a Master of Accounting and Finance, Bachelor of Finance and is a Chartered Accountant.
Leonie has 25+ years’ experience in botanic garden management, public realm development, community engagement, visitor programming, master planning, and infrastructure delivery. She holds a doctorate in taxonomy and palaeobotany, plus business administration and company director qualifications. She is the Deputy Director of Collections at the Botanic Gardens and State Herbarium of SA and a member of the BGANZ Finance and Risk Committee
A career spanning over 30 years in botanic gardens, Wolfgang is currently Director of the Christchurch Botanic Gardens and Garden Parks. He is a trustee of the NZ Gardens Trust and the Horticultural Ambassador for Grow Ōtautahi, Christchurch Garden Festival and a member of the BGANZ Member Committee.
Wolfgang has supported research for the World List of Threatened Trees before becoming Assistant Curator at Ness Botanic Gardens. He then became Curator of the National Botanic Gardens of Wales, later serving as Curator and Director at Sir Harold Hillier Gardens. He was trustee of Plantnet, UK and Ireland for 10 years.
John Siemon
Director
John is a Horticultural Scientist and the Director of Horticulture & Living Collections at Botanic Gardens of Sydney. John’s expertise includes plant physiology, plant breeding, tissue culture and germplasm conservation. As a leading expert in his field, John is committed to advancing the science of horticulture, preserving plant diversity and sharing his knowledge with others.
With nearly 30 years dedicated to Australian flora conservation, Michael has led major regional botanic gardens, securing substantial funding, fostering strategic partnerships, and developing successful volunteer programs. Currently managing Eurobodalla Regional Botanic Garden, he has held leadership roles in BGANZ, Aus Plant Society and a 3,000-hectare nature reserve.
In 2023 Michael won a National Garden Clubs of Australia Award for services to the community.
The Member Committee connects the broader membership with the Board, providing insights on sector challenges, trends, and growth opportunities. Consisting of members, it ensures BGANZ remains responsive, relevant, and aligned with its purpose.
Finance and Risk Committee (FRC)
The FRC advises the Board on financial and risk management, supporting oversight of financial affairs, strengthening risk and control frameworks, and ensuring compliance with legal and regulatory obligations. The committee is comprised of Board members with relevant expertise.
