Bickelhaupt Arboretum's 'Heartland Collection of Garden Conifers' located at Clinton, IA; Photo from March of 2004.
Hi Karin, I can solve this. Walter Erhard lists these synonyms for 'Plumosa Compressa' but lists a single 'Compressa', meaning, your plant has no synonyms at all. Chamaecyparis pisifera 'Plumosa Compressa' Hornibrook 1939 'Plumosa Densa = Chamaecyparis pisifera 'Plumosa Compressa'. Dax Erhardt, Walter - 'List of Conifer Names' (2005); ISBN: 3800148813
"C. pisifera 'Plumosa Compressa' Boom (1965); C. pisifera var. plumosa forma nana compressa Hornibrook (1929); C. pisifera var. plumosa compressa Hornibrook (1939), illegitimate (Bot. Code, Art. 36.1); C. pisifera var. squarrosa pygmaea hort.; C. pisifera var. squarrosa nana hort.; Thuya occidentalis 'Silveriana Nana' hort. (USA); C. pisifera 'Plumosa Densa' hort. (UK). O: Koster Bros., Boskoop, Holland (? date), as a sport from C. pisifera 'Squarrosa' I: C.B. Van Nes, Boskoop, Holland. Very dwarf, almost spherical shrub, with extremely dense, somewhat glaucous green, mixed foliage (yellowish green in Australia), eventually 0.5m tall. Illustrated in Welch (1979), no. 169 and van Hoey Smith (1989) p. 117. Both Hornibrook's names are appropriate horticulturally (Art. 27b); Boom's choice of the later one (Art. 27c) is sanctioned (Art. 46). See also C. pisifera 'Plumosa Juniperoides'." --The International Conifer Register, Part 3, RHS "'Plumosa Compressa' Hornibrook 1939 This low-growing plant, with very variable foliage, often close to f. squarrosa, has given rise to numerous undocumented combinations. Latin adjectives such as aurea, compacta, flavescens, glauca and nana, for more or less unstable mutations. The following ['Plumosa Compressa Aurea' H.G. Hillier 1971] is the only variation worthy of recognition." --The World Conifer Data Pool, The World Checklist of Conifers
