Current Collection Statistics

The living collection is the term we use when referring collectively to all accessioned plants growing at the Arboretum.  Arboretum staff are continually assessing and evaluating the health of the plants, their relevance to our mission, potential for invasiveness and their aesthetic value.  As a result of this ongoing assessment we regularly remove plants from the living collection for a variety of reasons, but our plant exploration, seed collection, and plant acquisition activities provide a constant flow of new plants into the living collection that provide opportunities for evaluation, research, study and appreciation of the beauty and diversity of the plant world.

The following chart shows data for the major groups of plants growing in the Arboretum’s living collection as of June 4, 2016.


  Families Genera Species Taxa Accessions Plants
Ferns 5 6 8 8 13 19
Gymnosperms 8 31 92 156 212 363
Dicots 89 255 761 1,266 1,639 2,531
Monocots 22 49 111 184 21 335
TOTALS 124 341 972 1,614 1,885 3,248

Understanding the Chart

The plant kingdom is divided and subdivided into successively smaller taxonomic units.  Family, genus (plural – genera) and species are the three most widely used by gardeners and botanists.  A family is a group of closely related genera and a genus is a group of closely related species.  For example, the heath family (Ericaceae) includes many genera, such as Rhododendron, which in turn contains many species such as rosebay rhododendron (Rhododendron maximum), flame azalea (Rhododendron calendulaceum) and Catawba rhododendron (Rhododendron catawbiense).


A taxon (plural – taxa) is a unit of classification, used here to refer to plants at or below the species level.  For example, Magnolia acuminata, Magnolia acuminata var. subcordata and Magnolia acuminata var. subcordata ‘Miss Honeybee’ represent three distinct taxa.

Acessions at PHA

PHA receives seeds, cuttings and plants from many sources over the course of a year.  Each taxon in a shipment of seeds, cuttings or plants is assigned when it arrives at PHA a unique number known as an accession number.  Each number represents a single accession and these numbers are recorded in our plant records database along with information pertaining to each accession.  The numbers allow staff to track the health, location and management of plants as they are propagated, grown, planted and cared for in the living collection.  The number of accessions in the chart indicates the number of accessions represented by at least one plant in the living collection.


Gymnosperms are seed-bearing plants of which conifers are the most well-kown examples.  Translated literally from the Greek, “gymnosperm” means “naked seed” referring to the manner in which the seeds are borne, often in cones or cone-like structures.  Pines, spruces, firs, junipers and cedars are some of the more common gymnosperms well represented at PHA.  Ginkgo, dawn redwood, Siberian carpet and the South American monkey-puzzle are some of the less well-known examples found throughout the Arboretum.


Dicot is a shortened version of dicotyledon which refers to one of two groups of seed-bearing plants known as the angiosperms.  Dicots produce two cotyledons, or seed leaves, and are represented by many of our most common garden plants such as oaks, hollies, azaleas, magnolias, asters and maples.


Monocots (monocotyledons) are the other subset of angiosperms and produce a single cotyledon.  Grasses, sedges, lilies, irises, orchids and palms are all monocots.