Bursera, named after the Danish botanist Joachim Burser (1583-1639), is a genus with about 100 described species of flowering shrubs and trees varying in size up to 25 m high.
 They are native (often for many species endemic) to the Americas, from the southern United States south through to northern Argentina, in tropical and warm temperate forest habitats.
Pulmonaria officinalis, common names lungwort, common lungwort, Mary's tears or Our Lady's milk drops, is a herbaceous rhizomatous evergreen perennial plant of the genus "Pulmonaria", belonging to the family Boraginaceae
Pulmonaria (lungwort) is a genus of flowering plants in the family Boraginaceae, native to Europe and western Asia, with one species ("P. mollissima") east to central Asia.
 According to various estimates there may be between 10 and 18 species found in the wild, but the taxonomy of this genus is very confusing.
"Bursera microphylla" is a North American species of tree in the Frankincense Family in the soapwood order.
 Bursera microphylla, known by the common name elephant tree in English or 'torote' in Spanish, is a tree in genus "Bursera".
 It grows into a distinctive sculptural form, with a thickened, water-storing or caudiciform trunk.
 It is found in the southwestern United States and northwestern Mexico.
A cohort study is a particular form of longitudinal study (panel study) that sample a cohort (a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time.
 A cohort study is a panel study, but a panel study is not always a cohort study as individuals in a panel study do not always share a common characteristic.
Bursera fagaroides is a species of flowering plant in the genus "Bursera" known by the common names torchwood copal and fragrant bursera.
 It is widespread across much of Mexico from Sonora to Oaxaca, and its range extends just into Arizona in the United States, although some sources suggest that it may now be extirpated in Arizona.
A liquefied natural gas storage tank or LNG storage tank is a specialized type of storage tank used for the storage of Liquefied Natural Gas.
 LNG storage tanks can be found in ground, above ground or in LNG carriers.
 The common characteristic of LNG Storage tanks is the ability to store LNG at the very low temperature of -162 °C (-260 °F).
 LNG storage tanks have double containers, where the inner contains LNG and the outer container contains insulation materials.
 The most common tank type is the full containment tank.
 Tanks vary greatly in size, depending on usage.
Zagłada Żydów.
 Studia i Materiały (English: Holocaust.
 Studies and Materials ) is a Polish academic yearbook published by a group of historians and researchers from the Polish Center for Holocaust Research created in 2003 in Warsaw.
 It is an annual devoted to the topics connected with the broadly understood Holocaust research.
 The target audience could include academics dealing with the Holocaust, but also college and university students, as well as broader public interested in this topic.
 Each volume forms individual and self-contained monograph.
 Authors of the articles represent various generations and scholarly approaches.
 The common characteristic is their frequent reevaluation of primary and secondary sources as well as the popular perception of truth.
 Important part of the journal consists of book reviews.
The Volkssturmgewehr ("People's Assault Rifle") is the name of several rifle designs developed by Nazi Germany during the last months of World War II.
 They share the common characteristic of being greatly simplified as an attempt to cope with severe lack of resources and industrial capacity in Germany during the final period of the war.
In United States federal anti-discrimination law, a protected class is a group of people with a common characteristic who are legally protected from discrimination on the basis of that characteristic.
 The following characteristics are "protected" by federal law:

Question: What common characteristic does the Pulmonaria and Bursera genuses have?
Answer: flowering plants